I didn’t fly at SW - but have good friends there.
If you told me you were dead set on living in PHX or DAL, I would say go to SW. Since you are dead set on ATL, go with Delta.

Southwest is a great company, and you can make MORE than enough money there. But there’s no way I would want to fly a 737 forever or have a 7-12 year upgrade. The options of aircraft and seniority at DL (And living in Atl) make the job great!