I have been in November many times. The weather is really nice, there is the food and wine festival, and the crowds are pretty light.
I have gone in December but it is early in the month - the first or second week. All of the special holiday decorations are up. The closer you get to christmas the more crowded it gets.
If you have to go just before the holiday, go before Thanksgiving. The week before Christmas will definately be more crowded. Just aviod the parks the day after - or go to Epcot, where larger crowds are more easily absorbed.