Resilio was there first actually, created by the Bittorrent company of old. The main con is it is closed source and less secure, depending on your threat model. Pro is it works really well, and is compatible with less skilled users.

I also came here to put in a word for Resilio. It's the fastest and most hassle-free thing I've found that doesn't require a server. SyncThing was always very slow to reconnect and update for me.