The verdict
We could easily rank the programs in terms of overall features and ease of use, but they all have their individual strengths. It’s not even necessary to choose only one of the options: you may want a different method of keeping your desktop and laptop in sync than for updating the media on your phone.
If all you want to do is copy files from one computer to another, Rsync, with or without Grsync for a GUI, is a good choice, but it falls short on the automation front as well as not handling two-way syncing at all.
Unison does a fine job of keeping two computers in sync, tracking changes made on both systems and keeping you informed about them. For interactive use, it’s the best of the bunch. Its lack of automation may be a disadvantage for some and not having any mobile clients renders it unsuitable if you want to keep the content on a smartphone, too.
BitTorrentSync works very well, it’s easy to install and set up and has a decent range of features and options. But, and it is a big but, this is the only one of the programs here that’s not open source. That may or may not matter to you from an ethical standpoint, but is something to bear in mind if your devices contain sensitive data and you want proven security.
OwnCloud is a massive program in terms of its features and needs a web server, which means you may need an always on computer. The desktop and mobile clients are lightweight and unobtrusive but the whole ecosystem is too much if all you want is file synchronisation. If you want more though, OwnCloud has it in spades and may be the ideal choice for you.
Syncthing is a fairly new project but it already has an impressive range of features that work extremely well. Updates are frequent and development appears to be proceeding quickly. It runs quietly in the background, once you have set it up you never need to bother with it, just leave it to do its thing, which it does very well.
“Syncthing is a fairly new project but it already has an impressive range of features.”