Not sure if you're refering to this December, but I'm going to assume you are.
After extensive research, I recently came to the conclusion that Nov. 30 - Dec. 7 would be the best time to go for my family.
Dec. 6 - 13 will be Pop Warner week, which can give you a few problems at the Value Resorts as well as POR/POFQ.
I would say my first choice would be the week after Thanksgiving, followed by Dec. 13 - 20.
However, if you're not going to be staying at any of the value resorts or POR/POFQ, you could actually make it during Pop Warner Week; as long as you don't mind seeing a cheerleader/football player here or there.
I chose Nov. 30 - Dec. 7 (Week after Thanksgiving) because typically, and I emphasize typically, crowds are the lightest during the week after Thanksgiving, and slowly increase week-to-week as you get closer to Christmas.
I hope all of my rambling helped.