Bronica. My medium format career started with a Yashica 124g, I sold this to buy a Bronica etrs. Sold the Bronica to buy a digi (DOH!). Being without a MF for sometime I was fortunate enough to be able to borrow a Rolleiflex T, and a Hasselblad 501cm. Then I purchased a Mamiya M645, this was a real dog, probably because of misuse and abuse by a previous owner, but it out me off Mamiya and I'm cagey about buying used now. I binned the Mamiya and bought a Bronica SQB.
Apart from the mamiya experience I'd be happy with any of the above, my primary reason for choosing a new broni over a used hassy was simply one of money, I very much doubt I'd be abke to justify buying lenses for the hassy, the broni is nearer my price range. (OK, so I'm cheap :-) ). I will say that I didn't find the hassy very intuitive to use, and I lost a lot of first frames. Fortunately I managed to not jam it up.