FreeFileSync is great in that you can see what is going to happen before you sync and if necessary change actions for certain folders - but it doesn't work wirelessly (as far as I know). It's also great in that it handles renamed and moved files/folders (usually) without re-copying them over.
Bittorent Sync is great in that it syncs wirelessly between pc and phone but sometimes it gets things wrong and there are lots of conflicts. For instance, sometimes the timestamps are out by a few minutes for some reason and it tries to re-copy everything over.
It also seems to go very slowly occasionally for no reason.