My main attraction to Yale is the small class size. As much as I like 99% of Columbia better, that's something I just can't get around.
For whatever that's worth, I visited Emory and Columbia and spoke to a fair number of faculty at each and the main difference between the two that I saw is that Emory is better if you want to "practice" public health while Columbia is better if you want to be a researcher.
I was accepted to Yale, Columbia and a few other programs and ended up choosing Yale. I spoke with many Yale students/alumni and they all spoke very highly about the program.
I currently live in NY, so leaving the city will be difficult, but I am excited to go to Yale which has a great campus (unlike columbia) where I can meet and interact with other students. I also found the faculty at Yale to be very supportive.