Proton Mail · Switzerland
This is the service I use personally for one main reason: practical privacy. Because Proton is based in Switzerland, it operates under very strict privacy laws. The company cannot read your emails even if they wanted to, and they do not scan your data to create advertising profiles.
You can start with a free account, which has some limits but is very secure. For daily use, the Mail Plus plan (approx. 3.99 €/month, billed annually) removes these restrictions. If you need more, their “Unlimited” plan includes a VPN, cloud storage, and password manager.
Usage is simple. The mobile apps are excellent, and on a computer, you can use their web interface or connect your usual email client using Proton Bridge. I recommend Proton if you want a complete, secure replacement for Gmail that just works.