I rented one last weekend, and I really like it. I did not have any real problems with the focus, though it does hunt in low light. I basically used the AF to get the focus in the right general area, and then modify if necessary. My exposures were good on both slide film and negative film. I used the 45, 80 and 120 lenses, and they were all excellent. Bokeh looked great, the lenses are fast, and they are built well. I am considering renting the Hasselblad soon to familiarize myself with it, but if I go for a 645 AF system, I think I will probably go for the contax.
One nice thing about the Contax is that it has a focal plane shutter, so you can actually use the fast lenses wide open outside. You have 1/4000th and f/2 as standard instead of 1/800th and f/2.8. Also, I can use my Hasselblad FE lenses on it, while the H1 has no shutter so I can't use the 110/2 or 50/2.8 which I already have. And of course, the hasselblad costs around 7000 for the kit, while the Contax can still be bought new for around 2800. The H1 viewfinder and autofocus are vastly better than the contax, but I am not so sure about the lenses. I am looking forward to the comparison I will make. Ergonomically, the H1 feels nice, but I would much rather have the normal shutter speed dial and aperture ring that you have on the contax. It just works better for me. I would consider the Pentax if it had a removeable film back, but it doesn't, which is totally unforgiveable for me. Not only do I want a digital option for the future, but I often shoot both black and white and color at the same time, so I always want at least two film backs. In 35mm rangefinders I carry two cameras, but that is not really practical with cameras this large. And frankly, other than hasselblad it is doubtful that any of them are more future-proof than the others. Contax is dead, but Mamiya was sold yesterday, and Pentax's future is questionable. I would rather have one shutter that might fail than one for every lens. But any way, those are just some reasons that I would probably go for a 645 if I went for a 645 AF.