Good question. Well formulated and clearly thought out. First, let me congratulate you on your acceptance to three very fine schools. I have a few thoughts:
Case study method -- Although case study schools like Darden and Harvard promote the usage of cases, for hard core finance courses they use textbooks as well. There are still cases used in every class, but they are typically short cases, grounded in the real world and heavy on numbers. I liked learning finance this way, because it was all real world stuff rather than theory. It made my investment management courses that much more interesting. Now to be fair, there are some people who really just want to spend time in the theory and in some respects you can learn more that way, so if that's more your style, lecture might be better for you. But, depending on how comfortable you already are with IM, you might enjoy more the case study approach. BTW, you'll be working a ton at Darden.
IM -- If you've been in IM and have connections then the brand of the school probably matters less. If you're looking at making some type of transition though, Darden will get you more respect. UNC is more regional in that regard. I think you should spend a little time thinking about which school is better for you and your career goals -- read both schools' career reports very closely. Where do grads go and in what quanitity. After you do that, then factor in the other stuff like your spouse.
Visit both schools -- If you haven't done it already, this is a must. It's amazing how many times just visiting a school will turn on a lightbulb that says "this is it" or this definitely isn't it. Whether it's a class, a conversation with a professor or run in with a student, visiting makes a big difference. It made a huge difference for both Scott and I even though we came to different conclusions, they were the best conclusions for each of us. And that's what it's all about.