I happened to find a Mamiya RB from a member of the local camera club at a good deal. Happy as heck with it and have no plans to switch to anything else.
If it had been a Bronica or Pentax I'd probably be just as happy.
What I have learned with time and use is that for me with MF an ever so slightly wide of normal lens, a 90mm on the RB, is my norm and my preference for most of my "out and about" general shooting.
I do have a 150 soft focus lens too, and it is really nice too, but it's like carrying a totally different camera when it's on. I hunt for very different, more specialized subject matter.
My question for you is; what are you planning to shoot?
The reason I ask is that for most of my MF shots; a TLR with a normal (80ish) lens might have been a better choice. Easier to carry and hand shoot, lighter, blah, blah blah...
I'm not trying to promote one camera type or another, just provide food for thought.