We visit every President's Week and every Easter Week. DO NOT base your decision on weather alone! Let me tell you the past two President's Weeks have been beautiful! It was in the 80's everyday and sunny, just gorgeous. This past April (week preceeding Easter) it was awful! It was cloudy and unbelievably windy. It was sooooo cold getting out of the pools that we didn't even want to swim. We had 2 out of 7 days that we actually saw the sunshine.
You cannot predict the weather, so don't base your vacation on that. In fact we just returned from our August trip and it was low 90's and very low humidity. The weather was beautiful. Every other year it has been crazy humid and rains every afternoon. Not one day of rain last week!
You may better consider the crowds. President's Week is busy Sat, Sun, and Mon. Then the parks and resorts seem to empty out. As a PP said, not everyone is off all week, but they are off on Mon. Easter is a busy time period. The week before and the week after. Heck, just look at the points required to stay! That will tell you how busy of a time it is!
We always visit those two weeks because I teach and that's when I'm off! I love it when Easter falls in March because our spring break is always the 2nd or 3rd week of April and we miss the Easter crowds and points!