I have really enjoyed Bittorrent Sync, but the new pricing tier and limited folders has me looking at Syncthing much more seriously now. It wouldn't cost a lot to pay for Sync Pro, just that it sort of irritates me.
Sync is really awful software, I've lost so many files and everyone I know has had corrupt files / lost work using it. On top of that it's not open source (so no chance of writing a version that's not buggy as shit) and now they want to charge money for P2P functionality (e.g. Unlimited folders)? No way.