All are challenging to ATL if you are Delta Connection. You would not believe how many DL retirees there are in FL (like, all of them!) and they tend to only list the night before a flight.

MCO, FLL, MLB are your best bets in order. MLB/DAB are very difficult due to the large number of RJs on the route. MCO has lots of AirTran flights as well and they are likely to treat you better than DL.

Good luck.