Haha.

Well I have the fastback, but I can tell you that the springer is.... a springer.  So it has that particular look, not sure if the added springs do much comfort wise.  But from seeing them in person, the springer seat is more narrow, and I can only assume would be less comfortable than the vintage wide.   It certainly seemed to have less padding. 

The fastback I have is considerably better than stock, but I still get saddle sore after a full tank of gas (100 miles-ish).  Not terrible though.  I assume the springer would be similar, and the vintage wide would be better. 

If you ever want a passenger seat, Id personally avoid the springer, as that would look pretty terrible IMO.  The fastback aint to bad for passengers, as long as its a skinny girl.  The vintage wide style pillion seat will handle the average and above average ladies.