I'm recommending Zane Lamprey's show, Drinking Made Easy on HDNet as a resource for drinking ideas in different cities.
In Atlanta, I would try heading to Sweatwater's taproom and TacoMac (the one located in mid-town Atlanta) as it has over 300 taps on their wall. Amazing!
Chattanooga has some places but I can't remember them. Nice chill dives around downtown.
Nashville is my hometown! Yazoo Brewery has a taproom (open on weird hours) but their tour is held on Saturdays I believe. You must get your hands on a beer named "Sue" as it's Yazoo's highest ACV%. Blackstone has great beer! The food is solid, but just go nuts with their beer (try Chaser Pale Ale and Nut Brown Ale). Boscos is a change of pace, but not my type of environment (try Bombay IPA). And finally, a great place for beer and some nice servers to look at is at Flying Saucer (over 200 taps on their wall). 12th South Taproom and Grill, Dan McGuinness, and Melrose Neighborhood Pub are some nice chill places!
When are you heading out to Nashville? I'll head back into town for the holidays as well.