Hi Laureen! Yes, Thanksgiving weekend has always been a very busy few days at Walt Disney World. But that doesn't mean you can't have a magical vacation if you plan ahead.
Try to get some
Dining reservations either in the parks or at the resorts and Disney Springs. Things have booked up quickly so don't be too fussy with the location or the time. Many families opt to eat a main meal early afternoon with breakfast at the resort and light snacks in the evening.
Crowds are impossible to figure out. The only thing you can go by is what has happened in the past. Thursday can be crowded or it can be less crowded. Friday and Saturday are almost guaranteed to be very crowded in the parks. Sunday is a so so day as many of the guests who have come for the week are departing.
I believe your best bet for parks are Animal Kingdom and Hollywood Studios. Both of these parks are more half day parks now with all the construction and new things coming their way. Epcot is a large park and can handle the crowds. The park to avoid is the Magic Kingdom as everyone will be heading there and if you can wait then its best.
Just make sure you do some dining and FastPass reservations and you will enjoy whatever park you decide and handle the crowds well.