Given they accept any input that presumably matches a regex it doesn’t matter which one you choose. But if you are looking for a new email provider and de-Google your life, I’m pretty with ProtonMail and their other offerings. Also moved my 2FA and Password manager to them, alongside their VPN.
proton has some issues that may or may not be issues for you - https://stateofsurveillance.org/news/proton-mail-fbi-stop-co... - http://thoughtportal.org/2025/02/26/proton-mail-says-its-pol... these people seem more problem free so far https://mail.tutanota.com/login
In the big scheme of things, I’d trust Proton more than Google and other big tech companies even if they aren’t perfect.