I've worked in both markets. Atlanta was a far better option for low income/sec 8 flips and rentals. Chicago was superior in everything else (value add buy/holds, appreciation, higher end flips, etc...).
I live in Chicago so that's the convenient market for me. The returns in Atlanta weren't so much better that the travel could be justified. All things being equal, Atlanta's low income neighborhoods felt safer, construction was easier (Chicago can be difficult during the rehab process), the rental laws are more favorable and financially, Geotgia is in better shape.
As for Chicago, there are several neighborhoods that are D+ to C- that can jump to B to B+ within the next 5 years. They are higher price points to get into, but once you get past the headaches of dealing with Chicago, the appreciation is more than worth it.
If you have any specific questions or if you need contacts in either market, feel free to pm me.