I do like BTSync and considered it, but I'm not the biggest fan of the idea that my data is stored on everyone's computer. AeroFS allows me some semblance of control, and as I grow, it will allow me to add users easily.
I won't know until I try it though, I could just as easily change my mind and use BTSync.
It doesn't put your data on everyone's computer. The data goes onto the computers that are sharing the folder. If you have two computers, the data is on two computers.
BTSync could be installed everywhere, but it only syncs between the folders with the same key. So if only your computers have your key(s) then only they would have contents of your folder(s).
I won't know until I try it though, I could just as easily change my mind and use BTSync.