Choosing the Private Cloud for secure file syncing
blog.aerofs.com
blog.aerofs.com
It's pretty much my go-to answer for small team file syncing. It probably doesn't make sense for individual users unless they're technically sophisticated with a lot of computers. For larger enterprise use, no one has yet asked me to set up file sharing, but AeroFS would be a top option I'd consider.
The biggest problem with AeroFS now is that there isn't a whole lot of adoption on the mobile API, so mobile apps tend to support Dropbox, iCloud, and maybe Box (if enterprise focused), but not "save to AeroFS".
Note for the unclued: rdl is the author of the linked article.
SpiderOak might be a good option, although there (like AeroFS) isn't much integration with iOS apps yet. Their security model and general thinking is probably the best of the public options. (Tahoe-LAFS is interesting too, but not really ready for prime time; it's a lot more like AeroFS in design with commercial providers added on.)
I still use Google Docs/Drive to share collaboratively-edited files with some people, and iCloud for iOS device backups, so I think the answer is there isn't a single answer.
Turtl is cool because the server is open-source as well, meaning you can use the hosted version (already all set up and ready to go) or install it on your own network.
If your files are properly encrypted you can safely store them anywhere you like, using whatever technology that best fits your usage scenario.
AeroFS is a great option for file-syncing. Compare public file sync (Dropbox), private file sync (AeroFS), and traditional network file shares (CIFS/NFS).
Can you risk files in the public cloud? If no, you're limited to just private file sync and traditional network shares. And this is where AeroFS can shine.
You may already have a network share. Its secure. But its a pain to access remotely (VPN) and mobile devices are not compatible at all. So you may choose to migrate your files into an AeroFS Private Cloud so you can sync files instead of browsing files via the network. Syncing files to your desktop gives you offline/remote access.
I'd argue the most secure option is probably leaving data where it already is. If you already have a file server, with permissions and such thats already vetted secure. Cloudtenna adds mobile file access to your on-prem file server. No need to migrate files to a new storage platform.
My blatant pitch aside, AeroFS is right solution if you want to replace mounted network file shares with file sync. Cloudtenna, instead, is good for adding the web/mobile access features of Dropbox to your existing network shares.
It really shows that they have experience transferring big files over the internet (via P2P). With Dropbox I often only get 100-300 kb/s upload, BitTorrent Sync maxes out my connection. Download is a similar story.
And with encrypted secrets the server part is easy too. (Obviously you've got to trust them, but I'm writing this on OS X so...)