We were fall visitors until DS got too old to take out of school for extended period of times, so we went to early June three years ago. I was worried about the crowds but was pleasantly surprised with the crowds not being unbearable. I did notice a few years ago, the crowds increased dramatically the weekend of Father's Day and thereafter, most probably due to all the schools being out. You know, Fastpass makes a big difference in the waits, now.
A good thing, at least for me, is that I can enjoy the water parks in June. The water parks are too cold for me in the fall. The bad thing is the heat is pretty intense compared to October. In October, though, you have to keep an eye on hurricaines. Ten to one, half dozen the other, huh?
When our kiddos get out of the house, I suspect we will head to WDW in the fall again because of the milder (a little) weather.