I fly delta a lot for work. I don't prefer to connect in Atlanta in the warmer months but thats mainly due to the weather. Twice coming back from Kansas city we were held at MCI due to ground holds in Atlanta because of severe thunderstorms. Aside from that, Atlanta is a big airport but absolutely fine and I have no issues navigating it. And I have had 0 problems with Delta. If I'm flying for personal reasons though I do usually book a non-stop flight and that's typically southwest for me.