The Midwest is cool and all...but I have to say, I went to CMU for a six week program, and I LOVED it. The food was pretty crappy, but the dorm I was in was really spacious and pretty, the campus was gorgeous and just close enough to the city to have plenty to do and just enough of its own bubble for it to be safe and beautiful. I really loved Pittsburgh. I think Pittsburgh gets a bad reputation for no reason, it's really a gorgeous city. And there are plenty of rolling hills around Pennsylvania.
Also, I don't know what spazman21 is talking about, leafy green hills at umich... the midwest north of a certain point is completely flat (melting glaciers and erosion flattened it and made it into rich farming land). I mean, it can still be pretty, and it's still green, it's just not hilly. At all.
So, I say you should go to CMU. But that's just my own personal bias and love for the school. :P
Also, about which one has the most prestige: They're all good schools. Employers (in the US, at least) will all recognize that you went to a respected university. Have you visited any of these schools?