Have you checked out the Unofficial Guide's crowd level chart? Go to www dot touringplans dot com, then click on "crowd calendar" in the left column (disboards won't let me post the link). It predicts that Animal Kingdom is the best park to go to and Epcot and MGM are the worst the day after Thanksgiving. They take everything into account when coming up with their predictions, holidays, day of the week, EMH, public school calendars, etc., etc.
Having said that, I'm going to Epcot that day! LOL, I should skip it and take my own advice but that's our first day, and it's our tradition to hit spaceship earth as our first ride of the vacation. We're also going to Epcot again later in the week, and will be following that chart more closely on our other days.
I hope that's helpful!