ATL is more centrally located for SE travel and DL probably has more frequencies out of ATL to other SE destinations than does CLT. Not sure how your travel will play out, but for example FLL-CLT-BHM seems like a routing that would add a lot of travel time to a trip. And FLL-MEM should be a DL non-stop if west TN is in your travel plans. Of course, ATL has its problems, but on the whole given the type of traveling you may be doing, I think it's better than a CLT connection.

As for which FF program suits your needs better, I cannot say.