Proton vs Sync vs Skiff

So I'm wanting to move everything from Google for both personal and professional work. I'm deciding between either Proton, Sync, and Skiff. My main goal is I have some sensitive stuff, especially professional, so if I need to put it on the cloud, I want is as secure as possible. My main hang ups for each service is:

* Proton: I've heard it isn't as secure as it claims to be.
* Skiff: Still new and based in the U.S. …

privacy proton skiff sync