Ok, I've got an opportunity to buy an RB67 later. However, I enjoy using the 6x6 square format. I'm still unsure whether it's possible to shoot 6x6 on the Mamiya RB. ideally it'd be nice to have one camera that can shoot 645, 66 and 67. Also, how do Mamiyas lenses compare to Bronica's. I've been using a C330S TLR and so far I've been unimpressed. It's a tricky decision.
I was so stunningly unimpressed with the C330 TLR I was given with a full set of lenses (65mm, 80mm, and 250mm) and almost every accessory that you could buy for it, that I traded it all in for a Hasselblad and never looked back.
Perhaps you will have a better experience with a RB or Bronica SQ-Ai