I'll hazard a guess that Thanksgiving would be much busier. My thinking is that in some parts of the country Columbus day is barely even a thing(i.e. the schools don't close in places I've lived) and pretty much everyone gets some time off for Thanksgiving. Also the Christmas decor at Thanksgiving is a big draw for many folks. You do have F&W and the halloween parties in October, and it is still very warm in Orlando at that time of year.
Since SWGE is opening August 29th, I don't think it'll matter. It'll be packed no matter what.