Been both.
Thanksgiving: particularly about Tuesday to Sat is very, very crowded, its packed, it is quite stifling most of the day, long lines, people everywhere, you will feel overwhelmed at times.
Christmas week: makes Thanksgiving look like a tiny, off-season crowd.
Imagine a coat closet 6 ft long and 3 ft deep. Thanksgiving is like trying to stick 6 to 7 adults in that closet. Christmas is like trying to stick 100 sumo wrestlers in there.
For Christmas at
DVC it is wise to make day by day reservations. For Thanskgiving just calling at 11 months out from departure date is fine unless you want a GV.