I have no idea when Easter is this year, but that week is EXTREMELY crowded (as much so as peak times during the summer). The week before and after is pretty bad too. Any other time in the spring is more crowded then, say, February, but not nearly as bad as June or July (plus, the weather's beautiful).
As for May, late May is starting to get crowded (Florida schools normally get out for the summer around May 21st, and Memorial Day Weekend is VERY crowded), but early May (the first week or so) has nice weather and isn't very crowded.