I considered both before choosing one. Ended up going with Protonmail because:
* The folks behind Protonmail are also heavily involved in the OpenPGP.js project. Interop with plain PGP from non-Protonmail accounts is on their roadmap and a feasible future feature. AFAIK that's not on tutanota's roadmap and they use a different customized crypto library, so all you'll ever get is e2e encryption with other tutanota users.
* Proton's mobile app is a top-rated android mail app, and pretty good even compared to iOS's Mail app.
* IMAP support is also on Protonmail's roadmap, but not something I miss due to the good mobile app.
* The tutanota.com and tuta.io domains are dorky and hard for other people to remember.
* The folks behind Protonmail are also heavily involved in the OpenPGP.js project. Interop with plain PGP from non-Protonmail accounts is on their roadmap and a feasible future feature. AFAIK that's not on tutanota's roadmap and they use a different customized crypto library, so all you'll ever get is e2e encryption with other tutanota users.
* Proton's mobile app is a top-rated android mail app, and pretty good even compared to iOS's Mail app.
* IMAP support is also on Protonmail's roadmap, but not something I miss due to the good mobile app.
* The tutanota.com and tuta.io domains are dorky and hard for other people to remember.