To be honest this answers itself. You'll notice that a medium format TLR (like the Rollei) do not exist any more, wheras medium format SLRs (like the Hasselblads) are still quite common. Unless you've got a special need for the TLR (which is quieter, faster, smaller and lighter) then you're going to be better with the Hasselblad. If you do theatrical photography then a 135mm Rollei would be a handy tool. Also, yes, you read correctly the Rollei is smaller! It's a taller camera, but it's smaller in each other way, there is a very long back focus on SLRs.
However the problem with the Rollei TLR is as you've mentioned it's not a system camera. If you want different lenses for a Rollei, you would need a whole separate camera. So if you wanted an 75/80mm lens then you'd need a separate Rollei 2.8 or 3.5. This is why Rollei eventially conceded and developed the SL66, and the 6000 series of cameras.
So over to the Hasselblad, they're a quality product and feel wonderful to use (but actually an SL66 feels just as good). There is a great choice of Carl Zeiss lenses, though only newer T* lenses are worth the money. I'd also advise you that you get the newer CM version of the 500. You should also be aware that Hasselblads are rather complex cameras, and they do have a habit of breaking down despite their good reputation.
While Carl Zeiss T* lenses (for both SL66 and Hasselblad V-system) are exceptionally good lenses, you should consider a Bronica SQ-a (and SQ-ai). The Bronica is just as good quality as the 500C/CM, however are half the price of the Hasselblad, and the Bronica lenses are no worse than their Zeiss counterparts. Just to leave you with a thought, the SQ-a should not be discounted.
There are a number of other worthy candidates to consider, there is also the Mamiya C-series (the C33/330 are good and very cheap), and the Mamiya RB and RZ. I didn't recommend the Mamiya RB/RZ earlier because it's weight is a major problem, with a good setup weighing considerably over 10kg, but it is a highly capable studio camera.