I think your best bet would be to visit Ann Arbor to get a good feel for the campus, preferably before school ends because it "feels" very different in spring/summer term. While I'm pretty familiar with the greek system in general and the area, I couldn't begin to name which chapters would take sophomores easily and it probably wouldn't be very Panhellenic to do so either. There are 15 NPC groups, 1 of which is currently a colony. There have been a few recolonizations/colonizations over the past few years, which generally increases the likelihood of upperclassman receiving bids. Sometimes those chapters are looking to even out the number of women in each class.
Since the other schools you are considering are in warm climates, you may want to think about the climate! While we had less snow and warmer temps than usual this year (less snow than they had in Atlanta this year even!), it does get quite cold and we get a lot of snow up here
I don't want to discourage you from Michigan, it's a great school and a great college town, the climate can be quite a shocker to people who are not used to it.