2nd the recommendation for the RB67, with the small qualifier that it's the only one I've used.
I don't usually chime in for these discussions because others have so much more breadth of experience, however, the reason I don't is because the RB has been able to do everything I've ever needed! (except street/stealth, for which I have my Olympus XAs) Literally every time I consider a switch or addition, I realize the camera can't do something the RB67 can. Operate without a battery for use in frigid conditions for extended periods or for extremely long exposures, flash sync at all shutter speeds (huge!!!!) for use with fill flash under changing conditions etc., exhibit minimal mirror/shutter shake for hand holding at slow shutter speeds (very well damped/governed mirror), do close ups without extension tubes (or extreme closeups with them!), exhibit stability under windy conditions with a good tripod (similar weight as a 4x5 without being a wind sail), preview depth if field, durability/repairability, great/bright waist level viewfinder, rotating back (huge!!!), changeable backs (huge!!!), maximize medium format resolution when making "standard sized" prints (very personal, but just saying...), all while having a full range of excellent and REPAIRABLE (C variant) lenses. And it's cheap! What other camera can make these claims?
I'm very glad it was my intro to medium format cameras, and it will likely be the only one I ever want or need. People say "its a studio camera" but it excells everywhere where stealth isn't needed. And enough about the weight as well, I'm no kid or bodybuilder, and can carry it, four lenses, all accessories, and a Marchioni Tiltall for 15 miles! You just need to, um, train a bit.
