I picked Pitt over Northwestern for two main reasons. Chicago is a great
place to visit, but not the sort of place I was ready to move to (a personal
thing I guess). More important was the sort of students that I encountered
at each school. Without saying bad things about the Northwestern students
I just liked the Pitt people much better.
As far as rankings, Pitt has been slowly climbing its way up and is ranked
by US News as slightly higher. The students here are amazingly smart, and
if you do well here, at pitt, there is almost no residency that you won't have
a shot at. The same can be said for NW. Almost everyone loves Pittsburgh.
One plus, if it is your thing, is that Pittsburgh is the organ transplant capital
of the US, if not the world, which makes for some interesting opportunities
for med students if you seek them out.
Good luck with your choice, but the final decision should be to follow your
gut.