i've been using both and can say that gmail does not prioritise user privacy and security as much as proton mail does. proton mail's list of security measures is long https://protonmail.com/security-details. these guys have end to end encrypted inboxes meaning even the company can't read your emails, proton mail is also based in switzerland so none of that NSA coercion google has been trapped in affects proton mail. we all know google's business model, on the other hand, though, right? scan all your incoming messages and bombard you with ads. i read on there blog that they also recently launched a tor website so as to add another layer of privacy for users. hope that helps.