Dab is right, Spring Break is a very hectic time to go. I was just there during this year’s Spring Break and it was CROWDED! We went a couple of years ago just after Memorial Day and it was terrif! personally, I think March is WAY too cold to swim, Spring Break wasn’t a whole lot better although the water parks had pleanty of guests. The last day we were there was in the mid-80’s.
If you’re not going to swim then consider autumn. I went once in October and another time in November. October had pleasant days and cool nights, a great change if you are starting to get cold weather elsewhere.