ExpressJet would be a good fit for ATL if that what you are looking for. But you may as well apply to Delta as they have a slight preference towards military pilots. Although you probably would not get ATL as your first base with Delta, not sure about XJT as they still operate separately for pilots (ASA & XJT).

You could try PSA or Piedmont as they too are close to ATL with their bases.

All regionals are running fairly short upgrade times with a few like Skywest, Horizon, and Envoy running a little longer than others.