I've been happy with pCloud which has Win/Linux/Mac/Android/iOS clients.
1. pCloud doesn't support file permissions or symlinks, thus you can't use it as a real filesystem (eg, building and testing software out of it).
2. pCould is a "cloud fs" (the files aren't on a host filesystem), whereas Dropbox is syncing a host filesystem. The difference is very visible in performance.
If the first issue was fixed (I've asked them many times, to no avail), I could live with the second.
In my experience pCloud works fine for me having the Documents, Music and Pictures folders synced, and having many other folders as cloud only.