Michigan no question...
The only think NU has that Michigan doesn't is a sitting US Supreme Court justice, and he won't be there much longer, and when he's gone NU's reputation and ranking will likely decline to more realistic levels as a result
That's quite the bogus statement. Having a sitting Supreme Court Justice does not impact the quality of a Northwestern Law School education. The school is top-notch on many legitimate bases, and consistently ranks in the top 3 for job prospects (NU uses a random lottery system with concealed GPAs to match its students with employers). You don't get that for having a sitting S.C. Justice.
Either way OP chooses, he will have the chance to obtain an incredible legal education