If you want ATL base, I'm guessing that means you may want to work at Delta in the future. In that case, SkyWest may be the best way to avoid the lengthy flow program and heavy metering going on at Endeavor. Skywest was (is?) metering, but not to the same extent as Endeavor. This would be a big consideration on my part, although we can't predict the future.
Frontier and Southwest also have bases in ATL. I would be trying to get on with them ASAP if possible, and then try to get hired at Delta, if ATL is the long term goal for you.