I'm an undergrad at Emory (although I won't be staying here for med school), and interviewed at Einstein a while ago.
I would DEFINITELY pick Emory. The school is located in an area rich in healthcare activities of all kinds, including the CDC, American Cancer Society, Children's Healthcare, and others. And although Grady is not on campus, it's still a great place to train.
Although I liked the students I met at Einstein, the facilities and surrounding area were not as impressive as what I was used to as an Emory undergrad.
That's the bottom line (a.k.a. my personal opinion)
I would pick Emory. I interviewed at both schools and will probably be at Emory, I think. Einstein, while a great school, is not everything that Emory has. The opportunities available to you at Emory are great. Also, Emory's reputation is better than that of Einstein's, if you care about such things.
Einstein's a good school if you're interested in working with minority/underserved. You will still get those type of exposure at Emory b/c Gradys is a county hospital. However, Einstein is literally surrounded by the poor.
Einstein's also P/F grading for at least the first two years, and its lecture hour time is one of the shortest in the nation.
Emory has ample opportunities for involvement in public health, and the school makes it very easy to pursue MD/MPH. The campus is really pretty, but then again, I felt that the student population is much more ethnically homogenious than many other schools I've been to.