We have been to US/IOA two times for Christmas. The theming is nice without being obnoxious. Stay for the Whobilation Show. We were at the HRH and enjoyed our stay. They had Christmas decorations and a menorrah lighting ceremony for each day of the Festival of Lights.
If airfares run some special, I have already told my wife I would love to do Universal or Disney in early December. From everyones descriptions they are decorated beautifully.