Is there any Dropbox-like service that lets you control your own private keys, without resorting to the ugliness of uploading an encrypted image to Dropbox?
It's important to note though that their client is not open-source, so if one goes through all that trouble to use end-to-end encryption, it seems a bit unsatisfactory to me to then trust this company to actually keep the private keys on my machines (and encrypt things correctly).
Personally I used syncthing which doesn't do encryption but also only uses my own devices, so I can keep the data on my machines at all times.
Tresorit is nice, but seems kind of pricy. Boxcryptor works well on top of Dropbox. Personally, I've switched to Nextcloud which keeps everything in my control, and it also supports e2e (though the e2e UX is still rough around the edges).
Even though it's proprietary, Resilio Sync does encrypted peer to peer sync, plus it allow encryption-only nodes. These contribute bandwidth, but cannot decrypt the data.