Wayne State and Michigan State are both great schools, so congrats on your interviews.
That being said, they do have different focuses.
Michigan State was founded to provide primary care physicians for the state of michigan. As a result, the school is heavily slanted toward pushing its grads into primary care (family practice, internal med, pediatrics, obgyn). Of course, this doesn't mean that you can't go into a specialty- the ortho resident who treated me when i broke my foot a few months ago was from msu, and ortho is one of the most competitive specialties right now. Michigan State also has a unique curriculum in some ways. They use a lot of problem based learning as opposed to traditional lectures, and also use prosections in anatomy lab instead of actually having students disect the cadavers themselves. Also, most students at MSU have to move after their second year to other cities in Michigan for their clinical rotations. This could be a plus or a minus for you.
Unique features of Wayne State include a huge class (almost 300 students per class, one of the biggest in the country) and a VERY urban location. Wayne is affiliated with the Detroit Medical Center. In my opinion, this affiliation grants WSU students some of the best clinical training in the nation. Right now, things are a bit up in the air between WSU and the DMC, as their contract is expiring and neither side seems to interested in negotiating a new one. However, I'd bet that they'll work things out eventually.
Bottom line is that both schools are great, but they are also very different. I'd probably choose Wayne myself, but that is just my personal preference.