I use the one that’s built in to the Fastmail service. I have a custom domain just for aliases. The Fastmail alias-creation API is integrated with the Bitwarden app (which I use) so that makes creating new accounts (that use email addresses as usernames) on websites really easy. I also use Spamgourmet which is free, convenient, and has been around a very long time. No custom domains there, but they let you use a variety of their domains and they have some short ones which is nice, but I do find that they’re blocked pretty often, mostly by major mailing list services.

While I’d love to add my opinion to the Play Store reviews, there’s no way in Hell I’m installing some kind of Christofascist malware on any device that I control.