This is just my opinion, but try to go to IOA on the warmest day because of the fantastic water rides that will drench you there. My wife and I were in Orlando for a week in early December 2000 and the highs were mostly in the low 60's. Fortunately, the day we went to IOA, it warmed up to the high 80's. I'm not sure if this was typical December weather in Florida or if we were just unlucky.