Wustl's grad program is actually amazing. I will def chose wustl over Umich. It even gives you more money. In fact, I would even say I even prefer Wustl's education than Columbia or Penn. 

A few years back Wustl's program actually got into top five. The ranking has dropped dramatically over the past years due to politics, but I will say it still has such an amazing reservoir of faculties. 

UMich is also very good. For me, however, it is not as good as Wustl. Perhaps if you are interested in robotic arms and such you could go to UMich. I might be very biased because I studied undergrad at Wustl and was more exposed to the teaching of its grad program.

Just my thought.

What you want as a student and who you are as a person should focus your choice. Whichever university you choose, know that every university goes through cycles of growth/ progress and failure/regression (depending on faculty / available courses / etc.) that will impact your experience there.

It's always good to flush out all your options, especially with scholarships. You could always reach out to Michigan financial aid to inquire if they will give you aid in lieu of WASHU's offer if you make a great case for it. Great financial aid is certainly an incentive.

U.Michigan typically ranks higher / more frequently than WASHU. Their student population will likely be more diverse....Michigan is often portrayed at the outset as "the fablab school" but they also have faculty like Perry Kulper that trickle drawing thinking/research into the pedagogy as well. I would recommend researching both schools on how they do their "thesis /final project" if that is a priority to you. I say this because WASHU senior/final project is a prescribed process compared to other schools....they require all grad students to locate their proposal and research within the context of St. Louis, MO and follow a specific process that doesn't allow for a lot of learning/thinking beyond the delivery of a "building".  Depending on who you are this can be a pro or con. Some friends I know there say WASHU might change that in the future, but perhaps not in your anticipated timeline(again something to verify on your own).