eww.. tough call. Only got interviewed @ Pitt, but I'll pipe in anyway. NUMS was originally a very top choice with U Chicago. I just have this thing for Chicago though I had never been. that said, both curricula seem similar, very little contact hours, lots of problem-based learning stuff.
As for the clinical experience and research opps, Pitt blows Northwestern out the water. Hospitals within a 50 mile radius? u frigging kidding me? NUMS doesn't have its part of the city to itself [U Chicago, Finch, Loyola, Illinois-Chicago]. The cities are on a different teir of price and size, so that's also personal preference. As someone that's never lived in a truly big city (Tampa doesn't count, yet) either one would be awesome for me. PBL schools seem to have very cooperative/friendly students so that should be close.
Either way, you're going to be somewhere great. Have a good time and don't look back.