We usually arrive the Wed before Thanksgiving and and as far as we can tell all of the decorations are up. Osbourne Light Show is running by then and the Candlelight Processional at Epcot usually begins the Friday after turkey day. Mickey's very Merry Christmas party (or whatever it's called)is one of the few things that doesn't begin until December. So either way you'll get to see most of the holiday stuff. That being said, keep in mind that Thanksgiving week is VERY crowded. Our kids are in HS and college so we can't pull them out, but if I had my choice I would certainly opt for December. Futhermore, if you're using DVC points you'll need fewer of them for the early December stay. We love DWD at Christmas but as soon as all our kids have flown the coop, we're going on our own - in December! One last thought, Thanksgiving at Disney is almost like a non-holiday. We've tried several options for a traditional dinner and were not really pleased with any of them. Lately we've been ordering the precooked turkey dinner from Goodings and adding the side dishes that we wanted. It's a little bit more work, but a better meal. Room service from Olivia's is convenient but very expensive. Twice we paid about $125-150 for dinner for 6 and both times they gave us 6 slices of pie! At that price they should have delivered at least one whole pie! Plus there was always too much of what we didn't eat and never enough mashed potatoes! Hope this helps....good luck!