The weather is really cooling off right now, but still pretty warm - high 80's. The crowds are relatively low, also. Not much wait in MK last weekend - sign said 40 min., but we walked right on with no wait & most rides were like that. EPCOT wasn't bad 2 days ago, either.
The only thing you may want to take into consideration is the 'love bugs'. They've been pretty horrible, but they are dwindling now, also.
Crowds, weather, bugs --- The end of Sept. on is really the nicest.