We were there June 2-7 of this year...it was SOOO HOT (97 and 80% humidity)!! Apparently from what other folks were saying we hit an unusually hot streak of weather.
We were also there for one day in April of this year (around the middle) and the weather was much nicer. I don't know about spring breaks on the east coast, but in the midwest they are all in March, so I would imagine that some of the spring break crowd might have dissipated? But I think Easter is late next year, I would definitely check that before planning.
Whichever you decide, have a great trip!