For the most part, Thanksgiving at WDW is 95% Christmas already. You won't have the Festival of the Holidays at EPCOT until the day after Thanksgiving, but most of the parks/resorts will be decorated the week of Thanksgiving. We used to go the week before Christmas but started going the week of Thanksgiving and prefer it. Mostly because it gets us in the spirit of the holiday season. We felt rushed with last minute Christmas planning when going the week before. I have not gone the week after, but I understand that it is mind-numbingly busy that week. You get the advantage of the Christmas parade without attending a party, but I'm done with Christmas after 12/25. I will say that we have always wanted to go to NYE, so that is an advantage if you go the week after and can stay through January 1.