Here’s a useful chart comparing all the popular cloud and email providers - eylenburg.github.io/cloud_comparison.htm

I use Tuta and I’m very satisfied with their services. It offers end-to-end encryption, it’s open source and it’s user friendly. The most common complaint you’ll hear from people about them is that they don’t offer IMAP. Personally I don’t mind it that much. It really depends on what you’re looking for.