A relatively recurrent topic. So, wiki page … and so it can get updated as/when relevant.

What is a registrar, etc. For some background, see, e.g.:
Wikipedia: Domain name registrar

Registrar that's just a registrar or …
all-in-one or bundled service provider. Some pros and cons, background, history, etc.

There are pros and cons with a company/organization/entity that's
a registrar and also provides other services. How many other
services, of what type, how closely related, how trivial and/or complex
is their also handling (all) that other other stuff, does it, e.g.
degrade or conflict with them offering better / more competent registrar
service - e.g what are their priorities, what do they mainly do, and
how (un)important is it to them to operate and maintain top-notch, or
at least quite darn good solid registrar services?

And, what, if any, other services does one want or care about? E.g.
does one only care about the registrar services … or does one actually
want/use those other (types of) services, and, e.g. does one want
a single provider or integration they offer - maybe that convenience is
more important than best of breed registrar services? Well, depends
upon one's use case.

E.g., both AWS.amazon.com* and cloud.google.com** are also registrars -
though that's not what they're mostly known for or do. And as
registrars, I'd rate both of them as at least "competent" … but
probably not best of breed nor top notch for registrar - though they
certainly beat out many. And of course if one is looking for ease of
integration with AWS or GCP, and that's the top priority, then those
choices respectively are a no-brainer.

There are also matters such as does one want all one's eggs in one
basket? Well, sometimes that's quite convenient … and if one is
sufficiently selective regarding basket quality, might not be all that
bad - and yes, again, does also depend upon use case scenario, and,
e.g. risk tollerance, and (in)tollerance regarding vendor lock-in, etc.

And Gandi.net - yes they do also offer/sell some services besides just
being a registrar - but primarily they're a registrar. Why do they even
also have that "other stuff"? I'm not sure - I'd guess they also have
many customers that want or expect that. E.g. there are lots of,
typically smaller customers, that want not only registrar services …
but they often typically also want the at least relatively bare
essentials to set up a web site (and possibly basic email for domain) -
so some bit of virtual hosting type services - be it VMs or just some
services and ways to configure that (and possibly also email) - and
some SSL cert(s), bit of storage, way to manage some at least
relatively simple DNS - and that's about it. Many, especially smaller,
customers tend to want/expect/"demand" that of a "registrar" - probably
mostly out of ignorance as to what a registrar is - and/or just wanting
the convenience of one stop shopping for some simple basic web (+
managed email) set up needs - where the customer otherwise doesn't have
(or want to bother with) anything of their own infrastructure-wise,
other than some computer(s) with Internet access (at least
intermittently), reasonable browser, and email - typically from their
ISP or some free email service. And they expect anything else needed
will be relatively trivial software they install or someone else will
host and provide it - even if they don't explicitly realize that's what
they're looking for. So, sure, Gandi.net has some 'o that basic goop
available too, but not tons of it, and certainly not what they
particularly push, but it's there if someone wants it. Gandi.net is
also a high volume reseller - they've got very capable API, and have,
for example, had (and may still have) AWS as one of their large
customers. Likewise direct customers - they have quite attractive
volume discounts - so if one has lots of domains, the prices become even
much more attractive - and of course they have API for ease of dealing
with lots of domains, automation, etc.

Anyway, not everyone wants the same thing and/or has the same use case
scenario … and that's okay too.

*AWS.amazon.com used to do (all?) their registrar services via Gandi.net
as a reseller - though that wasn't obvious to the customer (but was
visible if one looked carefully at the registry whois data). AWS has since
become a full fledged registrar themselves. Not sure if they still
(also) have any bits they maintain and/or resell (e.g. perhaps some
specific domains?) via Gandi.net.
AWS > Documentation > Amazon Route 53> Developer Guide "At the end of the registration process, we send your information to the registrar for the domain. The domain registrar is either Amazon Registrar, Inc. or our registrar associate, Gandi. To find out who the registrar is for your domain, see Finding your registrar."
**cloud.google.com registrar services has been sold off to and is now
owned and managed bysquarespace.com and, at least as of the time of
this writing, is still being transitioned fully over to squarespace.com
See also:
Squarespace Enters Definitive Agreement to Acquire Google Domains Assets
About the Squarespace purchase of Google Domains registrations
See also earlier: some pros/cons of "just a registrar" vs. provider of additional services

List of Registrars

Did at least mostly well fill out and organize fair bit of detail, for the curious/interested, some earlier background "discussions"(posts):

Various pro/con recommendations, including fair bit of supporting reasons
some comparing hassles vs. not of, e.g. toggling whois privacy, IPv6 glue records, Gandi.net/NameCheap.com/Joker.com
Gandi SAS (Gandi.net) acquired by Total Webhosting Solutions B.V. (TWS)

So, first note that Gandi SAS (Gandi.net) has been acquired by Total Webhosting Solutions B.V. (TWS) (https://your.online/). However Gandi has been exceedingly excellent, and thus far it continues to appear that won't be getting screwed up and thus far to Gandi customers things appear to continue operating as before - oozing competence, excellent service and reliability, "No Bullshit", web and API interfaces, domain, etc. continue as before, and hardly any change to be noticed at all - mostly have to hunt around web pages and such to even know any change at all has occurred. So, hopefully Webhosting Solutions is and remains smart enough to not mess with that, as that's primary driver that attracts and retains Gandi's customers, and if new ownership were to screw that up, Gandi's customers would scatter to the wind, and Webhosting Solutions would lose most all the value of their Gandi acquisition. Matter of fact, private equity firm Montefiore Investment had earlier acquired Gandi in 2019 and I don't think anyone noticed the slightest glitch or any drop at all in service or the like (I certainly didn't ever earlier notice - only catching that historic detail now about five years later).

So, Gandi has been and thus far continues to be excellent. They're very much "No Bullshit", and stand behind that. They ooze technical and operational competence, and essentially just work and damn solidly well. I've had zero negative experiences with Gandi. Heck, I've not even heard of anyone having any negative experiences with Gandi. And sure, they're not the cheapest registrar out there, but I find the value highly well worth it. It basically just works exceedingly well, in all regards, and continues to consistently do so. Well worth it in the savings of headaches and problems and incompetencies etc. with many other registrars - just one such glitch with some other registrar, in the value of one's time, could quickly eat up years or more of the value of any such monetary savings with many such registrars - even the moderate annoyances and crud of many other registrars, well worth the slight extra price on Gandi to avoid the bullshit of over registrars and be able to operate much more cleanly, efficiently, free of hassles, glitches, problems, frustrations, etc. And Gandi is very reasonably priced for the value one gets. Can even get significantly discounted prices if one is a larger volume customer. Gandi also supports Debian, giving all Debian developers Gandi's deepest discount tier pricing that's otherwise only available to their absolute largest volume customers (historically they let Debian developers have domains entirely for free). I also attended a Linux install fest in San Francisco that Gandi hosted at their facilities, so Gandi does give back to and support Open Source.

In approximate chronological order, I'll lay out at least many of the ways I've been impressed by Gandi.net. And haven't had any negative experiences at all with them (or even heard of such!) - so that itself probably also says something about them too.

Supports Debian - I think when I first ran across the info (and they may even run based on Debian? - but I don't know regarding that), they allowed all Debian Developers to have domains for free! Last I checked they no longer do that, however they make available to all Debian Developers their highest discount tier pricing, regardless of the number of domains any Debian Developer has with them.

Not sure if they still have offices in San Francisco, but they at least did (and probably have at least some presence in the US? Though they're headquartered in France - I think they may be located where and such that they're mostly not under the claws of US law (at least regarding controlling domains), but do fall under EU and GDPR). They hosted an Open Source event at their offices there in San Francisco - Yes, Ubuntu California San Francisco QA Jam 2015-02-08

Really everything I've heard/read about Gandi has been positive - or at least certainly not negative.

Even before I had any domains or services on/from Gandi, when I was just setting up an account on there (required before, e.g. having domains there - and can have an account there and no services/domains - no cost to simply create account there) - I ran across a slight bug in their interface - notably setting up account in US, and dealing with states. I reported the issue to them. They fixed it in quite quick order and were great on communication and follow-through to check and ensure that all was well and I was no longer seeing the earlier issue I'd reported - pretty impressive response for a non-paying (or at least not-yet-paying) customer. I looked up that much earlier issue for the details and went (summarized) about like this:
2015-01-23T04:55:34Z I opened issue and got automated response (RT support-en #5534422)
2015-01-23T10:21:23Z I received notification they'd transferred it to relevant support area
2015-01-23T16:12:40Z I received notification indicating it was resolved
2015-01-23T19:06:27Z I checked, not (quite) resolved and notified them
2015-01-24T15:06:33Z I received notification they'd forwarded to specialist
2015-01-26T16:19:28Z I received notification they'd applied work-around on my account (effectively fixing it for me)
2015-01-26T18:31:36Z I checked confirmed all good (not only work-around but bug fixed)
2015-01-27T16:16:55Z I received notification confirming that they'd solved and fixed the issue
This is vastly better than many registrars, when one often has to do battle with them and go trough 2 to 3 rounds just to get them to even understand or acknowledge that there's even an issue, after which other registrars may still fail to fix the issue and/or often provide incorrect information. And I got that great level of service from Gandi when I wasn't even a customer yet and for a relatively low priority pretty minor bug.

Their No Bullshit slogan/motto really does very much apply. No gimmicks, tricks, clean interfaces, they don't shove bunches of advertisements and stuff like that in your face - generally only the slightest mention of some offers - when they really are special/bargains - and generally only see that on their web site, and pretty dang unobtrusive - generally have to click or follow a link for more details on stuff like that - so it's generally only a small notice on screen - and easily dismissed - and won't come back and be nagging one. And no promotional/sales/marketing/etc. emails - unless one opts into that stuff.

Renewal and other official emails - you don't get other goop (unless you explicitly opt in). The emails have exactly what's needed and very well laid out. E.g. got a domain that's heading towards expiration? Yes, you get the email - you also get in the Subject: what domain, how long until it expires, and body of the email tells you when it expires including timezone, and it also spells out exactly what happens and when if the domain isn't renewed - no guess work, and quite useful Subject - especially among the many other emails one might typically be looking over. Essentially their communications, including email, also of quite high quality. Amazing how many other registrars can't even manage to reasonably do that even with their renewal emails - bloody hell, many such from other registrars they can't be bothered to even put the domain name in the Subject nor there indicate how long until it expires or when it expires.

As I'd similarly quite say of Debian, "It just works" - pretty much rock solid clean, well thought out, and about bug free. Generally anything one needs to do with domains on Gadi, it's quick, easy, efficient - at least to the extent feasible (notwithstanding some mandatory periods for some operations and such - but it goes as fast as feasible - unlike some registrars that'll drag it out as long as they can get away with - e.g. like when transferring a domain away).

They do continue to improve their interface - it was never bad in my experience, but they do add/improve features which are actually useful (well, at least to some/many) - e.g. pretty easily allowing one to split up and delegate various parts of registrant/domain administration (e.g. billing, whois, DNS, etc.). They also typically don't instantly force interface changes on users - can generally use both the latest and greatest … and also prior generation interface for quite some time after the latest and greatest becomes available. So, no jarring forced fast hard changes (Atlassian, et. al., are you listening? … no), likewise they don't break stuff (again, unlike Atlassian).

GDPR - I think they handled that about as best feasible. Yes, the default changed (and they may have had to do that for practical and/or legal reasons), but if you want that data public - easy peasy - no support tickets, or emails, or trying to pass clue to clueless … the stuff basically just works - unlike some other registrars where that's quite the battle to achieve - or they don't even allow for the possibility!

glue records - likewise easy peasy - copy, paste, click, done. And yes, IPv6 too, no problem at all (wish I could say that for all registrars, multiple registrars are poor to grossly incompetent at that).

DNSSEC - likewise easy peasy. Again, wish I could say that for all registrars.

Quite same applies for any data one needs to change, e.g. whois, DNS delegation, etc.

Oh, and another data point for Gandi's rock solid reliability and dependability and quality API, etc. When AWS entered into offering domain registration via their Amazon Route 53 service offering, AWS didn't themselves (at least initially) become a registrar, but resold Gadni's registrar services through AWS's Route 53 service.

I might be forgetting some details and further examples, but pretty much solidly rocks, excellent service, and quite reasonable price for the quality.

NetworkSolutions.com / Web.com - avoid like the plague. They may not be the worst out there, but they're pretty horrible. Some of their sh*t:

• Tons of marketing/sales/spam email, difficult to opt out (have to call a phone number and can take up to 30 days to opt out!).
• Overpriced - their default pricing is horrible. But if you play the song and dance with their offers (e.g. yearly at renewal), you can get a reasonable price (just start to go through the motions like one is going to transfer the domain away - then you get offers for a reasonable price - about market rate and about 1/3 what they'd otherwise charge). But alas, to take that offer, you have to opt in to their marketing emails … and yeah, opting out … ugh.
• IPv6 - last I dealt with them on that they still rather sucked, if I recall correctly - e.g. I think you had to do a support ticket to do IPv6 glue records … at like about a decade after IPv6 was very much a thing on The Internet.
• Interface lacking - there's just a whole lot 'o stuff that requires a support email or call to get done, because their interface can't - and you tend to get fair amount of incompetence, and lots of sales/marketing when dealing with them on phone or via email. Oh, yeah, and their web interfaces also pushes lots of sales/marketing goop - essentially lots of advertising for their own stuff all the time.
• Sometimes they'll opt you in for stuff you didn't ask for and don't want … e.g. just gave you a crud yourbasedomainname.somecrudTLD without your asking or wanting … then they of course want to sell you on renewing it. Ugh.
• They also tend to push lots of announcing clueless offers. Got sf-lug.org? How 'bout buy up all these sf-tote.someTLD and sftote.someTLD domains, I mean tote is like lug (as in sf-lug for San Francisco Linux Users' Group), right? Ugh.

So, yeah, general experience with NetworkSolutions.com / Web.com has been quite negative, with negligible exception.

Joker.com - their interface looks like a bad late 1990s web site loaded up with ads. Their interface also isn't very functional. And sometimes they just suck. E.g. GDPR … yeah, can't opt out of the privacy goop for whois. Need to change glue records? They were absolutely completely utterly incompetent at that - not only could their interface not do it, but the information they provided was incorrect, and even with numerous support tickets, they couldn't manage to to it. It wasn't that hard, change some IP address(es) on the glue record - they just couldn't manage to do it at all. Comparatively with gandi.net trivial to do - copy, paste, done - and IPv4 and/or IPv6 - all easy peasy on gandi.net.
See also:
done: proposed: sf-lug.org. change registrar from joker.com to gandi.net
proposed: sf-lug.org. change registrar from joker.com to gandi.net
proposed: sf-lug.org. change registrar from joker.com to gandi.net
registrar domain expiration notices - e.g. Joker.com vs. gandi.net ... & bit 'o registrar comparisons
GDPR & whois: SF[-]LUG & domain(s) Re: Domain ...

Godaddy.com … uhm, probably just don't. How 'bout start with their sexist/racist/… sleazy crud advertising (YouTube: Washington Post: GoDaddy's most controversial Super Bowl ads, and The Onion can't help but to take a well deserved parody shot at them) … maybe they're better now on that? I haven't particularly tracked. They're also based in Canada, so if you have some serious issue/dispute with them, and want to take legal action … good luck with that (at least if you're not, e.g. a Canadian resident or citizen). Been a while, but last I dealt with them their interfaces were rather lacking. Some of their behavior may be or have been shady - at least I've heard such - but didn't run into that personally. Oh, but one thing I have repeatedly seen, that's quite shady, and as far as I'm aware they're still doing it. So automatic renewals … no biggie, right, should be quite straight forward. Yeah, … the way they do those … they actually do the renewals slightly after the domains expire. Yeah shady as fsck - basically completely and totally exposes one to the mercy of GoDaddy every single time they do that. They don't even renew day, or hours before expiration, but only slightly after expiration.

Namecheap.com - sucky interface, and not so competent staff. Ugh, 2022 and they still can't do IPv6 for glue records on their interface … even though they have support requests open to do that for more than a decade! So, have to do support request for that … ugh, really, in 2022 … and they're not very competent about handing it at that. Oh, and API … 2023 and still: whitelist at least one IP before your API access will begin to work. Please keep in mind that only IPv4 addresses can be used. Also much of the information their support staff provides is incorrect … ugh.

AWS.Amazon.com offers registrar service via their Amazon Route 53 service offering. As far as I've been able to tell, they've always been competent at that. And, for better and/or worse, that's just a very small part of what Amazon and AWS does. So, yeah, most registrars (or their owning companies) don't also ship about 1.6 million packages per day. So domain registrar certainly isn't Amazon's, nor AWS's core business. But if one wants, e.g. tight convenient integration with AWS, well, they certainly have that. Of course if one wants to put all one's eggs in one basket, best be sure it's a damn good safe secure basket. Of course since AWS has quite ample APIs, it would be very feasible to use AWS as registrar, and do so quite independently, and well integrate that in with other things in interoperability. But then many registrars offer good/excellent APIs, so that's hardly something that's unique to AWS. Also of note. when AWS first offered registrar services, they resold through Gandi - which also speaks to Gandi's great reliability and dependability and quality APIs. Not sure if AWS still also does that, but at least since those earlier beginnings between AWS and Gandi, AWS has also become registrar in their own right, so AWS may or may not still also be using (reselling) Gandi's registrar services.

So, Google Domains has been a competent reliable registrar. However, on 2023-06-15 Squarespace concluded an agreement to purchase the Google Domains business. So, what has been Google Domains is being migrated over to Squarespace. And, though I'd expect that for the basic registrar services that would continue to be functional (but may be a bit different), it's certainly not being an entirely smooth transition for many customers. But that may mostly be due to differing interfaces, and that Google Domains offered services beyond that of registrar which Squarespace doesn't offer at all. E.g. Google Domains, in its DNS offering, has supported hosting of Dynamic DNS (DDNS). Squarespace has no such offering, so there are many customers not so thrilled with such changes, and many have been scrambling to find suitable replacement services. Note historically and generally, Google often launches things, and later drops them, as/when they find/decide they're not (sufficiently) profitable and/or don't well (enough) fit to their core business model, etc. So, although Google was quite competent as registrar, I find it no great surprise that they're exiting the registrar business. Do I see that as an issue with failed or reduced integration with Google Cloud / Google Cloud Platform (GCP)? Not particularly, as that can probably be integrated with the API of most any registrar that competently makes such available, without too much difficulty.

DreamHost.com - most notably gross technical and operational incompetence. Having been screwed over multiple times by DeamHost.com's hosting (see: Many times that DreamHost.com majorly and repeatedly f*cked up hosted data), there's no way in hell I'd trust 'em, let alone with anything at least potentially as important/critical as a domain and the registrar's responsibilities thereof. Even though they offer some services for free to 501(3)(c) non-profits, my best advice would be, even at that price, far too costly and dangerous/hazardous, wouldn't want to touch 'em with a ten foot pole, and I'd strongly recommend running away as fast as feasible.