OK, I am not trying to be baised at all, but seriously everyone says us Alpha Gam's have the best house at UMich for fraternities and sororities. Its has one of the best locations to classes and its just gorgeous overall. I would say that Sigma Kappa and Chi-O tie for sororities. For fraternities I would have to say Beta, Chi Phi and FIJI's house the LXA is renting out.
www.umich.edu/~greeks