Another vote for the Mamiya 645. I am a Mamiya fan, have the RZ67 and will be adding a 645pro to the stable in the next few months. IMO Mamiya seems to have very well thought out systems and the lenses are fabulous and pretty inexpensive. I don't think you could go wrong with the three 645 systems mentioned. I have no experience with the Bronica 6x4.5 system but they have a good reputation as well.