First thing first, you cant make a bad decision here. All of them are good bikes, and non have serious flaws. Yes, 636's have the most race like features, while the 600RR's have the most street. But a 636 will still do great on the street, and a 600RR will do fine at the track.
That said, the 600RR is my favorite. The steering a heavier, so it doesnt feel flickable, but once you lean it, the stability is great. I'm faster on those bikes than I am on my zx10, just becouse of how forgiving it is. Its the easiest bike to go fast on.
The seat is made of plywood. It sucks. Bad. But you could always get a corbin replacement.