I would base it on whether you want the special events around New Year's or not.
Based solely on crowds, the first couple days of the December/January trip would be crazy, but might mellow for the final days. November might be considerably less busy than 12/31-1/2 or 3, but probably steadily busier than 1/4-5.
If you've never done it, New Year's in the World Showcase is amazing and so fun.