I would say if all you care about is having a nice looking, fully-featured, easy to use client, Proton is good, but if you really just need... an inbox with an email attached, then Tuta will be a little cheaper and just as private, just with less bells and whistles.

If you care about removing yourself from other services like calendars, cloud storage, password managers, etc, Proton is way better since it has the full suite.

For example, Proton supports auto-categorizing mail (e.g. newsletters, promotions, updates, transactions, etc), unlimited email aliases, a more modern UI, good integrations with Proton Drive and Proton Calendar if you decide to use those as well instead of Google Drive and Google Calendar, etc.

Tuta is more just an inbox that you can bother to sort as needed, comes with some aliases if you feel like it but probably not enough for every single online service you have, has a basic calendar, but doesn't have any kind of integrated Drive access (is still in closed beta rn), and has a more... basic UI.