I have owned and shot Bronica ETRSi, Pentax 645, 645n, and 645nll, Bronica S2a, EC, and Hasselblad 500cm 6x6 cameras and a Mamiya RZ 6x7 camera. I have handled my friend's Rollie SL66 and Pentax 6x7.
My favorite medium format camera for portraiture was the RZ. My favorite camera for everything else is the Hassie 500cm that I currently own.
I didn't buy the Hasselblad. I took it in on trade and was pleasantly surprised that all the hype was true. In my opinion, over all, it is the best medium format camera out there. The Hasselblad is very versatile, has great build quality, excellent optics, is lightweight and simply a pleasure to use. The only downside is cost.