I'm somewhat new to MF, but for portrait/studio work the two Mamiya cameras, RB and RZ are great for that kind of work.
The RB67 is the older of the two. It is fully mechanical. Advantages are a removable and rotating back. The biggest disadvantage is that its a BIG, HEAVY camera. If its going to sit on a tripod in the studio, thats not a problem thought
The RZ67 is a newer electronic "super updated" version of the RB. It also has a removable rotating back, and a variety of lenses to choose from. The camera is much more electronic than its predecessor so it allows for AE modes as well as fully manual.