Hi -
I have no experience with the Bronica, but I own both a Pentax 67II and a RB67 plus the best lenses for each camera. (I used to own a Pentax 67 also).
There are pluses and minuses to each camera. For sheer cost, the RB67 cannot be beat as you can put together a setup for very very cheap these days. If you like shooting with waistlevel finder, then the RB67 is great with the rotating back feature, something I wish the P67 had. Also, the changable backs on the RB67 make it very nice. The downside of the RB67 is the weight, and it is considerably more than the P67. I am not one of the people who tell you it is not handholdable - it definitely is and I do it all the time - but that being said, I much prefer to handhold the Pentax, which is also heavy, but nothing near the RB67.
For image quality, the Pentax SMC lenses are superior to the Mamiya C lenses, sharper with much more contrast (if you like contrast). I prefer the Pentax lenses. But many of the features of the RB67 are more convenient.
I generally use the RB67 in the studio on a tripod, and the Pentax 67 in the field.
Keep in mind one other difference, which is that Pentax 67 syncs at 1/30th of a second, unless you buy the leaf shutter lenses, so if you do alot of fill flash, that can be a problem.
I my perfect dreamworld, there would be a Mamiya RB67 body that is light as the Pentax and takes the Pentax lenses.
At the end of the day, however, both cameras are very good, tried and true MF systems and will deliver excellent results.
If money is more of a problem, you can get more bang for your buck from the Mamiya.