Sounds like you do have a choice. If I did, I'd definitely go for the fall. Beautiful weather (barring hurricanes) and low crowds most of the time. I did a back to back Easter trip in 2002 (the week before and the week after with two different sets of grandkids). It wasn't unmanageable, but definitely go early and get out of Dodge around lunchtime. We went to MK one evening and I just about panicked; the people were so on top of one another.
My grandchildren wanted to go next spring break, which falls on Easter also. At first I was willing, then it occured to me that our Easter trip was the first Easter after 9/11. I felt the crowds even then, and I know it would be much worse now.