I'm ATL based and although I live there, about once a month I'll go back up to Chicago to visit friends or family. Usually I go into MDW and have never had a problem. The train ride from MDW to ORD is about 1:30-1:45. AirTran does a really good job getting pilots on board if DL is booked up for me. When time doesn't let me go into MDW, there's enough flights to ORD with enough carriers that I'll always get there eventually. Last Sunday I got on an 20:25 Frontier flight, no issues, plane not full.