OP, we went the first week of May and loved it. It's been a few years since that trip but if I could go any week, that would be it. The highs were around 88 and not very humid so it was nice to visit a water park but not so hot you couldn't stand the regular parks. Easy packing knowing you won't need long pants at all. Crowds were low.
I do recall a bazillion love bugs on the day we went to KSC but not at WDW.