I'm in the same sitution, minus the HST option. Are you sure HMS isn't giving you any need-based money? They do have the unit-loan thing, but it depends on your EFC and still will be more expensive than UMich w/ scholarship...
I'll be revisiting both schools, and right now I'm very impressed with both of them. I have plenty of personal reasons in favor of Michigan that likely don't apply to you, so I'll focus on those that may matter: concerns over classmates, opportunities during medical school, residency options, and access to academic medicine.
As I haven't revisited, I can only go on what I've noticed at the interviews and through email w/ a very small minority of the class, but both seem to have awesome students. Interests outside of medicine, diverse backgrounds, really motivated and yet know how to have fun, etc. This is a big deciding factor for me, and should be for you as well. Revisits will help you with this more than anything else could.
Most people have covered all the "opportunities." HMS may have some that won't be available at UMich, but not many. You could easily fill your time at UofM with Galens, other student groups, an international trip, research for a summer or a year, shadowing physicians, relaxing in AA or at football games, etc. and still have plenty of things you didn't do but could have.
Match lists are hard to read. If your heart is set on an MGH or other east coast residency, go to HMS. If its set on a west coast residency, go to a school on the west unless you don't have that option, in that case go to HMS. If you simply think you'd "prefer" a coastal residency, but don't have your heart set on it, UMich can get you there. Especially more likely for you since you've already proven yourself w/ the scholarship offer. And as another said, ~50% of the UMich class is made of Michigan residents, and many of the others will be other midwesterners. A high percentage of them WANT to stay in the midwest (I have no problem with it, for example). They match into amazing specialties still, and may have had the option to go to a coastal residency, but they wanted to stay in the midwest. Those that do leave have gotten into good residencies on the coasts, check out the match list for yourself if you want. Basically, the desires of the students at each school are different. HMS will, I'll agree though, give you a better shot at top residencies. You (and I) have to decide if that insurance is worth the extra cash.
Academic medicine is a big goal of mine, and I know both schools can get you into it. On one hand, I realize HMS is going to be better at doing this. Students there simply have the opportunity to make more connections, associate with more leaders, get better LORs, and work with "better" researchers. This is where HMS shines, in my opinion. But I do think it's hard to compare just how big that difference is, you'd have to talk to someone who's spent 1+ years at BOTH schools to get that information, I'd think. And one thing I'm thinking is that not only will the decreased financial burden of Michigan make it easier to stick to the academic path (take a lower paying job), but also allows more freedom to seek those "extra" opportunities in med school (year-out research, international trips, maybe an MPH) that would be hard to do knowing the interest will just keep growing while you're taking longer to finish school.
PM me if you want more information or just to chat about the pros/cons of either choice again. Hope we'll see you at second look(s)!