Why has no one mentioned the Cliff bus yet? For Emory students, I think it's vital to know about it.
The Cliff bus is funded by Emory (at least all their money finally went to something useful), and it is free to the public. The people on there are friendly and diverse. It's definitely slower than a car, but it's useful. It connects the Decatur MARTA station and Emory's campus, so it is feasible to live in Decatur/somewhere near a MARTA line. Personally, I adore downtown Decatur and would recommend living there. It's so friendly, tons of restaurants and independent stores, all the basics you need.
I take MARTA to/from working on campus every week, and it's okay, but people hitting you up for change are often not disabled. It is also not rare to see (or be) a young woman feeling uncomfortable who is riding alone. I've listened to men ask young women if they're married, have kids, can have their number, and I've had some unpleasant experiences being followed off the train by men asking for my number. The last one took the cake - as I waited to be picked up, he grabbed my hand, told me I "looked lonely," and would not immediately let go of me when I started tugging on my hand.