We go in september! It is awesome!
The weather is hot for some .... those who come from where it does not get very warm, and have no humidity! But I imagine all of the summer months are this way!
Everyone thinks september is hurricane season, but in all reality, hurricane season lasts from either june or july, through november!
The parks, are practically barren! NO crowds

at all! The longest line we stood in last time, 2003 was space mountain, line was roughly 13 mins long!
Mission Space, we walked on each time! morning, noon and nite!
So, as far as we are concerned, we will always go september!
Plus, it is low season, and you can save a substantial amount on hotel/house rental!
gabby