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

Will likely well fill out and organize remainder later, but in the meantime, some 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)

Will likely well fill out and organize remainder later.

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 ...

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.

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.