We picked this past April 28th for our Disney wedding because it's one of my favorite times to go. You can't beat the weather.. it's not super hot and humid and it doesn't rain a lot. Crowds aren't super slow, but it's definitely one of the less busy times to go.
Sometimes the cheer and dance competitions fall during this time of year, which can bring large groups to the parks. Doesn't really have much of an effect on overall crowd level though.
Epcot looks absolutely amazing during the Flower and Garden Festival and it's not crazy crowded like Food and Wine