Thanks Mad Dog,
Our vacation start from Dec 14 when we fly into Orlando, to Dec 30 when we fly black. From Dec 15 t0 Dec 20, that are the lowest days on the crowds calendars 7/10 and 8/10, we are going to Disney and Universal.
Plus we have 3 day tickets for any SeaWorld parks. So we are planning to do 1 day at SeaWorld and 2 days at BuschGardens, we are only interested on the roller coasters on those parks, and we want to pick from Dec 21 to Dec 29 the two days with the lowest crowds, one of those two days for SeaWorld and the other lowest crowd day for Busch Gardens.
So the plan so far is Sunday 22 SeaWorld and Busch Gardens Monday 23 and Tuesday 24. But if Christmas Eve would have slightly less crowds than a Sunday, even if it wasn't reflected on those calendars, we could do SeaWorld on the 24 (Christmas Eve) and Busch Gardens Sunday 22 and Monday 23.
I was really expecting a local, or someone with experience visiting Orlando parks at his time of the year to help me out, but I guess with the data that we have available at this time, there may be no way knowing any of this.