There are pros and cons to visiting at most times of the year. My real favorite is spring, but it is almost the most expensive time of year and tends to be quite crowded. Summer to me is the worst time of year: hot, crowded, and not especially inexpesive, plus there are those pesky storms.
Fall is nice; good weather, low crowds, and reasonable room rates.
Winter has low crowds, but the temps are too cold for me. I want to be able to swim for one thing. The parks just aren't (much) fun in a parka.
Christmas week is not a time I'd want to be at WDW. Too cold, too crowded, and I just don't want to mix Mickey and Christmas too much. Christmas is fun already. Going shortly before Christmas can be fun...but you run a risk even as early as October of getting cool nights.