Hey cmsmstp, I didn't interview at Sinai (I went to Einstein and NYU, didn't really like either of them, figured Sinai would be more of the same), but I definitely thought Emory was awesome. Of course, I'm biased...I grew up down in the ATL. But even so...it's a sweet place to go to school. Students are fun (did you meet Yair when you were down there? he's a badass), faculty is excellent, Mary Horton does a great job as administrator. I really liked it. Atlanta was the only city that could have lured me away from New York (but didn't in the end since I didn't think Emory had a reputation comparable to that of Columbia). It's nice to have the undergrad campus right there (more social facilities, more clubs/activities...the gym is impressive as well.) I also got the impression that Emory is really on the rise...they've taken a bunch of good faculty from other schools, plus they're pouring a lot of money into research. They could easily be a top 15 med school in 10 years. My impression of Sinai, however, is that they're starting to fall off a bit.
The one big problem with Emory: full grading scale!! My buddies in the first year class seem to be working way too hard. Yes, Emory kids kick ass on the boards, but it's because they've been having their ass kicked for two years by having to worry about getting A's (instead of just going for that gentleman's P). Also if you're in for some serious clinical experience, working at a crazy public hospital (Grady) could be good for you...but I don't know if it's for the faint of heart.
Anyways, I have a natural bias towards Atlanta. Weather is great (and when it gets hot, everything has air conditioning, unlike New York), girls are good looking (and the ratio, while not 9:1, is pretty damn good), town is fun (lots of restaurants/bars)...it's a sweet place to live. I definitely want to move back down there at some point. However, I love living in New York as well...I just want to make it clear that I don't think you could go wrong with either location. I know it's a tough choice, but I think I would say go for Emory.