My fiance and I have been there twice in the recent past, and once was at the end of June and the other time was in the middle of July. On both trips we had a great time and we never felt like it was crowded at any of the parks there. Our longest wait in line was 20 minutes for Space Mountain on the Saturday when we were there, asides from that wait our longest wait was only 10 minutes long! And we hit the rides like thunder mountain railroad, splash mountain, alien encounter, tower of terror, any coaster or thrill ride you can think of, and the tours as well. So we basically hit the long wait rides and got lucky that not a lot of people were there for the weeks when we were there.
So its kind of hit and miss. I have been to Disney 11 times in my life, 9 with my parents and sister and we used to go during spring break and I remember big crowds and long waits. I think you just need to decide what time works best with your budget and schedule and cross your fingers!