Proton for me.
Unless you’re E2EE, email is inherently insecure. And since most people aren’t using an E2EE service, let alone the same one, switching providers is only tangentially beneficial (IMO). If Proton gets hacked, you're still secure, that’s good. Otherwise, Proton can’t read your message, but Google can on the other end, so it’s not that different.
Full disclosure, I pay for Proton, but the security benefit (for me) is the ability to use a single email inbox with a forwarding alias through Pass (or SimpleLogin) for every account. Whenever HomeDepot or T-Mobile get hacked for the fifteenth time, I don’t have to worry about every other account under the sun because my real email address just got doxxed.
I’m not of aware of other service providers offering that integrated benefit, which is why I think Proton is “best.”