Cloudflare Domains is soon a thing (meant to be available from later this month in waves to current Cloudflare users, my guess is it should be available for all start of 2019). That might be nice. Cloudflare promises not to charge more than how much it costs them to get the domain, so they are dirt cheap domains, and Cloudflare has a great reputation for tolerance/no censorship - so you don't have to be worried about having your domain terminated/suspended.

Currently, namecheap is also quite popular, it's not especially elegant but it's cheap and secure. Tends to be my personal choice. I would immediately point your DNS to Cloudflare, after purchasing a domain, and manage your domain's records from Cloudflare.

Also worth checking out: https://www.gandi.net/ and https://njal.la/

Usually, namecheap is a safe bet. That'd be my recommendation, currently.

I find http://domains.google.com to be the simplest.

It comes with built-in privacy protection* and a free email forwarding service. So all emails to hello@yourdomain.com could be forwarded to your email.

* with recent news around Google + privacy, I'd take this with a grain of salt.

I recommend either IWantMyName or Namesilo. They have great support and no B.S. upsells a lot of providers have. I am not affiliated with them, just a customer.