I use quite a few, for a variety of reasons (including to become familiar about them for my writing at NameTalent and on my personal blog). I have only listed below comments for registrars that I have actively used.
Namecheap - majority of my names are there, love their CyberMonday promotions, good prices on many ngTLDs all year round. I have 100+ there and have used them a lot for years for both legacy and ngTLDs. I don't need their assistance often but when I do their staff are courteous and prompt. Transfers in and out work smoothly (have done a number of both). Love that privacy is included without additional charge. I use their Marketplace to sell (and occasionally buy) domain names and that you can list a newly registered name on their marketplace within the 60 day lock period.
DomainCostClub - I started a membership in the fall. I like a lot that across many legacy and new extensions you get wholesale prices all in one place. I have not made any money yet on their affiliate program but it seems generous. I find their search among the fastest and most intuitive. Love the clarity of their pricing (although note that the ICANN fees are not included). You do need to purchase a plan. You can significantly save with them if you have premium renewal domain names in particular. I wish they did not charge 5% for PP and CC payments. Privacy is included. Interface for your domains is intuitive. Note however that autorenew I think always comes in on position with new registrations, so be sure to turn it off (if you want to).
Epik - only starting to use them but they have great rates for NP designated accounts on a variety of extensions, and love how easy it is to set up a domain for sale on their market. Their CEO plays active role on NPs which is huge plus. Like the pluses they include without additional charge. I plan to have more with them in a year's time. Epik have Sedo and Afternic network support.
Alpnames - mainly just a few ngTLDs where they have the best rates. Very smooth interface for setting forwarding and DNS. Find their system of listing domains and seeing at a glance the dates, status, etc. one of the easiest to use. I wish they offered privacy and wish they had a marketplace.
Dynadot - I only recently started using them and only yet have 3 there. I found setting up an account there as smooth as it possibly could be, their rates are competitive across many extensions. The marketplace they have, that seems active sales wise, was one reason that I started using them.
NameSilo - long a popular choice growing rapidly. Their interface is liked by many, I don't find it quite as attractive and intuitive as some. I do like that privacy is included in their already great prices. Their prices edge even better if you meet the conditions (deposit a set amount) to be in their 'club'. I only currently have a couple there, but view it as a good choice for domains you plan to renew for many years. Their marketplace is easy to add your names to and has reasonable rates. I have heard from others who sold there. They also support Sedo MLS and Afternic.
GoDaddy - well if you have not yet used the $0.99 coupon your first domain name should be there! I like a lot that they have the (arguably?) most active sales platform and end users know of them through advertising and are more accepting a push there compared to the others on this list. On some extensions their prices are competitive. Afternic integration a plus. I wish most renewal pricing was more competitive. If you just have a domain or two and want to host it at the same place it is registered, an option like GoDaddy and Namecheap is good because of their hosting operations. So for certain extensions I register there - only have a few right now.
Name.Com - I only started using them at time of their CyberMonday deals that were great. I found registering names with them easy. Have not yet done much else as my names are still under 60 day lock. I have about 10 there. One of them I am using for development, and the DNS setting was easy to implement. Sedo and Afternic integration nice feature. They have regular promotions that are normally a good deal.
I also use two Canadian companies, but only for .ca domain names.
I plan to check out Hexonet and Porkbun at least as well in 2019. Welcome suggestions for others that I should try.
There are many excellent choices for domain name registrar. I have just listed a few of them here.
Bob