Our first two years we went in June. Our schools get out between the 3rd and 8th usually, but I was afraid to book as soon as school gets out because of "snow days"--if we go over 5, they automatically tack them on to the end of the year. We also have been in July of 02 and 03, including July 4 in 03--pretty crowded!
In 01 and 02 we also went for 4 day weekends in EARLY December. We left early Thursday and returned late Sunday. I took 2 personal days to do this (I get 3). The airfare in 01 was the best ever due to 9/11--only $135.
At the end of 03 we spend 2 days in NC and then drove down for 4 nights, including NYE, over Christmas break (but have to have Christmas itself in Ohio). NYE was the worst crowding ever but we just left Epcot at 7 and went back to the contemp. to watch the fireworks. Downside was driving back, leaving Jan. 2 with a few thousand others!
December is great, but planes are so iffy if you have to deal with cold, ice, snow, etc. This next year we will be back finally, probably July 10-17. It's value season, but not too close to my next year starting around Aug. 23.
Robin M.