I registered my first domain through Namecheap in 2015 and since then I have never used any other domain registrar. There was a time when I had over 30 domains with Namecheap but these days I have just 5 domains.
I wouldn't say I have a "favourite" as such, I used to use GoDaddy when I was younger and run my websites.
I've registered a couple of domain names lately for upcoming projects with Names.co.uk, simply because it was high in the Google listings and they had a special offer for cheap registration fees. I only need to buy the domains and set the nameservers, I don't bother with any other services domain providers provide as they're generally sub-par and overpriced.