While I haven't been able to use any of the AF 645 cameras extensively, my initial impression with the Mamiya 645 was that it was slow, awkward, and tended to hunt-focus a buch. The Contax 645 wasn't much faster, but seemed to lock on better. The Hasselblad H1 actually seemed fast, but is rather outrageously priced so that takes it down a notch in my mind. Haven't played with the Pentax 645N, so I can't comment on that. Had I to choose between all of them, I thin I'd probably go with the Contax. The AF isn't as fast as on the Hasselblad, but you get an extra stop of lens speed out of the 80mm and that's enough to compensate in my mind.