I've shot with all three major systems you're inquiring about (Rollei, Hasselblad, Mamiya RB/RZ). I had a Hasselblad system for years - loved it. One of the greatest advantages to it is the fact that it is a system - you can, with time, patience and money, find all kinds of weird specialized accessories and lenses to do just about anything. I went through a phase where I was shooting mostly large format and the Hassy was sitting unused, so I sold it on to someone who would get more use out of it. Later, I swung back and started shooting medium format again. I bought a Rolleiflex 2.8E off of Ebay for $500. It needed a good CLA (clean, lube, adjust), and my initial experience with it didn't bond us, so it sat for a while. I picked up an RB67 thinking I would shoot portraits in the studio with it. I have shot with it sporadically, but it is a camera that does not encourage spontaneity. It is a huge chunk of camera. I have only two lenses for it, the 90 and the 180. But that and three film backs (one of which is the motorized 6x7 back) weighs at least as much as my complete Hasselblad system (500C/M body, three backs, 50, 80 and 120mm lenses, AND a Superwide with the dedicated 38mm lens!). Which brings me back to the Rolleiflex.
I had it sitting around, needing a good servicing. So I bit the bullet and took it in and had it given a complete once-over. Now it sings like a canary. My concerns over its issues dissolved. I shot a bunch more with it and found that it really complements my way of seeing and shooting. I was concerned about the "limitation" of having only one lens though. I asked around here about opinions of using it as a travel camera and some kindly folks pointed me to the work of a number of famous photographers with Rolleis. I realized that the "limitation" was mostly in my mind. I've since traveled with it extensively, taking it on trips to New York, Paris and Toronto, and shot with it extensively around town here at home. It makes a good portrait camera, it is fantastic for street photography, and is one of the most portable medium format cameras short of a folder. You're not going to shoot sports/action with it, you're not going to do 1:1 macro with it, nor are you going to shoot wildlife. If those are your interest, a different camera would be better.
If you're interested in a system camera but are on a budget, look at the Kiev 88 - it's a knock-off of the Hasselblad 1600F with a focal plane shutter. Lenses for it are excellent and dirt cheap. The most recent versions of it are not ergonomically horrid, and if you get one that has been rebuilt by Hartblei or ARAX, the quality and reliability while not up to Hasselblad standards will be quite good.
My money, obviously, is on the Rolleiflex (I actually now have a matched pair of them, 2.8E models... they're nearly 60 years old and still going strong). But they're not for everyone - you may not like the ergonomics, or the twin-lens way of working. But don't let the "only one lens" consideration make you think they're limiting in some way. Look through my gallery here on APUG - if it's square, then 99% likely it was shot with a Rolleiflex.