We were there last year for the last few days of April into May. We loved it. Perfect weather, and crowds were not bad. We normally go in Sept, and the crowds were not quite that low, but still easy enough to plan if you use FPs. I don't think I would ever go during spring break. I hate crowds, plus the weather can be iffier. We went once during spring break in college, and had horrible weather. In late April last year we had mid 80s with no rain and no humidity for the entire 10 days we were there.
Good luck. We are going back at the end of April this year to get another trip in before our APs expire. We also love the Flower and Garden show at EPCOT and can't wait to see it again.