I started with Mamiya 645 Super, Rolleicord V, went to 645 Pro, then went to RB-SD
To me, decision was a combination of:
Modularity (repair by swap)
It was impossible to meet all of them at the same time. So by going RB, I sacrificed portability. I figured since going Mamiya 7 was out of my budget, anything else I choose with 6x7 size wouldn't be significantly lighter. (I wanted 6x7 film format) It's do'able but heavy. I have no experience with Pentax 67.
Modularity/repair by swap is an important factor for me. Sending a MF camera components for repair/CLA will cost just as much or often more than buying another part on second-hand market. So I had to choose a system that's highly modular.
Many people as the same question as you do (OP). What's the best MF camera for me? All of those threads pretty much ends the same way. Just about every make and model gets mentioned and OP is left confused. One good thing is, if you buy wisely, you can pretty much get most of what you invest in it back when you sell.