The Admirals Club in ATL is very nice and efficient.

I have done many MR trips through ATL and haven't had any issues. I can't speak for checking luggage, but the time between T and D is very quick. I was able to walk it in about 10 minutes.

For a data point - GF flew through ATL last week on AA. Security was a mess, and she had pre check. She said the wait was about 45 minutes.