We go during slower times- our favorites are:
November- anytime except Thanksgiving week. Great weather- high 70s during the day, mid 60s at night. Crowds vary from very low to the low end of moderate. Food & Wine Festival the first half of the month,
MVMCP and holiday decorations starting the second week. Free dining available most of the month.
October- the last week. The first 2 weeks are still hot and humid, and the crowds have really picked up in recent years. Halloween week is better- crowds drop off, weather cools down, and the
MNSSHP and Food & Wine are going on.
January through mid February- low crowds, low prices. Weather can be nice, or you can freeze your tushie off. Attractions can be closed for rehabs.
May- except Memorial weekend. Moderate crowds. Very warm, but not as humid as summer/early fall. Flower & Garden Festival at Epcot.
We haven't been during December (DH works on retail, so no vacation days allowed then), but we have heard the first 3 weeks are a good time to go- low crowds, MVMCP, all the Christmas events and decorations are in full swing. Weather is usually pretty nice during the day, but can get chilly at night.