The one that comes free with my domain registrar.

I also like Riseup but it needs an invite. I also like mail alias services like SimpleLogin and AnonAddy. People should use those more often.

I don't like how Gmail's tagging system works (All Mail and no "archive"). As for Proton and Tuta, I don't like how I can't use other mail clients other than their own web interface. If you only access mail via a web browser, then it's fine I guess.