I used [large american registrar], but switched to a small one in my country because I wanted to pay a local business. I found it from somebody's compilation of companies that offer a TLD for my country, and I just picked the recommended one in that post. It was the one that charged the least.
Keep in mind that with a smaller registrar you won't be able to get a TLS cert using the "do some shit with my domain records" method - you'll have to always install the nginx/Apache etc. plugin for Let's Encrypt