I personally prefer Chili's over the Budweiser Brewhouse (next to the Crown Room in the center of A)...better food and service from my experiences, plus you don't have to deal with the obnoxious smell of cigarette smoke.
As for what to do at ATL
, you can get a good workout just walking around the concourses. I'd grab a meal, and just walk around...lots of Delta action, but a decent amount of AirTran...
As for service, it's nothing to write home about. You'll get the snack basket on LGA
, where you get the choice between a few things (sun chips, crackers, granola bar, etc.); on ATL
, there's the snack box (oreos, cheese and crackers, etc.) and the snack basket later on during the flight.