I have always loved the big bold pictures they produce. I was at a gallery yesterday and I seen the works of John Humble and that was it. It was a field trip with my photo class and I was talking to the teacher about Humbles work. My teacher only uses medium format and she said it was a good way to go for that kind of urban photography. I was surprised that she didn't use digital at all.
I love his work, what do you all think.
http://www.johnhumble.com/
TLR's have their merits, but in your case I would go with an SLR.
So there are SLR's with inserts, and then SLR's with film backs. With inserts, you load the insert with film and then put it into the camera. It allows you to pre-load rolls of film. With backs, you load a film back with film, and then attach the back to the camera. This allows you to remove the roll of film from the camera mid-roll.
Examples of 645 camera with inserts include the Pentax 645 and the Mamiya 645E.
Examples of cameras with backs include the Mamiya 645 Super/Pro, and the Bronica ETRS/i.
I currently have a Pentax 645. Though I love it, I will soon be replacing it with a Mamiya 645 AFD (which accepts backs). My gripes with the insert system are as follows: 1) Polaroid backs are too expensive for insert cameras. 2) I don't like having to finish the whole roll once I load it. 3) I can't remove and store IR film in the field without a changing bag (with inserts, you're screwed once you load a roll of IR).
Remember that MF SLR's (except for the insert-based ones) tend to be modular. i.e. the body, back, and prism are separate. This can cause you to encounter added expenses when it comes to metering. For example, insert-based 645's have a fixed prism and metering built into it. But with a back-based system, you're typically looking at an extra $100-$200 for a prism that can meter. If you have an external meter, or don't need an internal one, that's a non-issue. But having a built in meter has its advantages for quick shooting.
The choice is yours.