I have a lot of domains registered on Gandi.net I don't have a lot of experience with other registrars, but they were recommended to me many years ago as an "ethical" choice
Reasons: They're straightforward with pricing, throw in a good if basic email service for each domain (two addresses), customer service is responsive and technically competent, provide a useful newsletter but are not pushy with it.
I also use Gandi. So far no problems (but I'm not very picky). I think the main reason to use Gandi was that I could search for any domain without the fear of it being bought the next day by squatters. I don't really like their web UI/UX though.
Reasons: They're straightforward with pricing, throw in a good if basic email service for each domain (two addresses), customer service is responsive and technically competent, provide a useful newsletter but are not pushy with it.