It shouldn't be very crowded the first two weeks of May. You picked a great time to go. I would say any day will be fine except Saturday, but even Saturday shouldn't be too crowded.
If possible, I would definately avoid going to Universal or Islands of Adventure on a Friday, Saturday or Sunday. The parks can get very crowded no matter what time of the year. Definately try to go Monday through Thursday.
How about the first weeked in June? Oy...I'm just cringing awaiting your reply as I'm sure it will be crowded. *crossing fingers...lol* I'm just hoping that it won't be as crowded as Disney parks.