Earlier quoted context omitted.
How about one for "I dropped DropBox in favour of an option with client side encryption"? Wuala, SpiderOak, even GDrive/DropBox + EncFS/Ecryptfs/BoxCryptor. So many better options than DropBox for those of us with privacy concerns. And for the more DIY people, there's OwnCloud, git-annex assistant (which supports encrypted remotes!), SyncThing and TahoeLAFS. Anyone know of a good sync client for TahoeLAFS though?
I don't see BitTorrent Sync in your list of alternatives. I've not used it myself, but I've heard good things about it. I just wonder if it's secure at all, given the open nature of BitTorrent itself.
I didn't take my RE any deeper, but trust it at your own risk. I'd recommend SyncThing over it as a good open alternative, though it's admittedly not as polished yet.
Admittedly I am listing several closed tools, but only those I've had good experiences with.