Hey socialepi,
I've decided on Harvard, due to the combination of a full funding offer (whew!) and staying close-ish to family. (umm, and maybe the name, just a little) It's also a great match for my interests - methods, neuro, and environment.
I did my MPH at Emory, and don't have anything negative to say about it. There is a thriving social epidemiology and global health program there, and a huge contingent of HIV researchers (many affiliated with the CDC). There is also a large group, led by Susan Allen, that focuses exclusively on HIV programs in Africa (http://www.rzhrg.org/index.html). They are always hiring students for research programs, and many do a 1-year internship in Africa after their MPH. I seriously considered Emory for PhD, and would have stayed without reservations.
That said, all of those programs you mentioned are world-class. I know the least about Tulane, but I know they have a famous tropical disease epi program. UNC and WashU are, with Hopkins and Harvard, generally considered the "top" epi programs (WashU was my second choice). And Michigan is my undergrad alum, and I know they have a large infectious disease epi focus, and are famous for their social epidemiology researchers. So this is probably no help at all
Enjoy your decision process!
(p.s. don't discount the importance of the city where the program is. atlanta is great, but not for everyone. same for new york.)