There are so many great medium format cameras that it's hard to go wrong. I personally prefer interchangeable lens cameras, mostly because 75-80mm is one of my least favorite focal lengths. If you think you can be happy with a single focal length, it's really hard to beat a TLR, and I would look at Rolleicords, Minolta Autocords, or an older Rolleiflex model (the non-letter models can be find for reasonable prices if you are patient). People love Yashicamat's but I have had negative experience with their build quality-- probably just bad luck on my part, though.
Have you given thought to 6x4.5 vs 6x6 vs 6x7 (or larger)? I personally prefer 6x6 because it is a unique ratio to work in that is specific to MF cameras, but it's really a matter of taste.
If you secretly want a Hasselblad but think it is too expensive, I've heard nothing but great things about the Bronica SQ system.