We went last July, last 2 weeks, and had a fantastic time. We hit the parks early, getting there before they opened, did the attractions we wanted to do, then blasted out. Crowds were noticeably bigger by dinnertime but by then we had done everything we wanted to do. Lines were not existent first thing, the longest line I saw was over 2 hours for Soarin' late afternoon but again when we went first thing we were straight on and got a fast pass for an hour later. Water rides got extremely busy later on too, roughly about 60 minute wait but again first thing you could just stay on and ride again.
I enjoyed my first visit in July, I loved the heat and are going back exactly the same weeks this year again. However, once we are not tied to kids' school/college holidays we will go at different times of the year. We have enjoyed going in February.