Emory is fantastic, both the school and the hospital! You'll do your first two years at Oxford and then move to the Atlanta campus in North Druid Hills. It is VERY expensive. However, they have an excellent financial aid department at the Atlanta campus (if possible ask to see George Lunkin as your financial aid advisor; you won't regret it) and the school receives a lot of money from Coca-cola. Not to mention the amount of connections that just being at Emory affords you. The rate of students finding work after graduation is outstanding.
Mercer is a good school, I've heard. But I don't know much about their medical school. I assume you would be going to the Macon campus, which I personally don't like. But that's subjective and not relevant to what you need to know.
Overall, Emory is one of the best schools in the southeast. I guess it depends on your ambitions. Don't sell yourself short!