Depends on your threat model. If all you want is to get away from Google / ad-tech, ProtonMail is fine, as are many alternatives (FastMail, etc.).

ProtonMail is also probably fine(-ish) if you want to escape mass surveillance from US and allies.

If you're worried about a nation-state actor targeting you specifically, then no commercial provider will fit the bill.

Whatever you choose, my recommendation is to buy a domain name and use it with your new provider. It will make it much easier to migrate providers in the future.