I currently live in atl. Did grad school at Miami Ohio and spent some time in C-bus. have a brother that spent 3 years in NYC (harlem/west village).
I don't think that you will be disappointed with any of the cities. they differ in size and cost. obviously C-bus won't have the night life of NYC. However, don't forget it's a city of 1 million with a major university. There are things to do.
I would prioritize the decision press like this:
1. the program and the professor guidance for your research. It will shape your future whether you teach or work in a chemical field.
2. Assistantship options. I did not pay for any of my grad school focused on academia. you should get the best funding possible. student loans are real.
3. cost of living- since all of the cities are fun, student loans are real.
4. visit and feel whats right for you as the final piece of the puzzle.
as for info on ATL- it is quite hot and humid in the summer. think of a bad summer day in NYC or C-bus and thats what you get in atlatna for every summer day. however, its 70 and sunny here in the spring and the winters are between 35-45. so you're trading better winters for slightly worse summers. the food scene and nightlife are very solid in ATL. visit GA tech, run the beltline/freedom parkway trail. Check out the westside provisions neat GA tech and roam midtown to grant park.
That will give you an idea of what's immediately around GA Tech. there are lots of other neighborhoods and to-do's just like there are in any large city.
Enjoy your decision. Undergrad is the new high school diploma. Grad school will truly shape your life.