I have been in all the months in question save for May. April and March have too many single guys, which kills the vibe and as a result the party isn't amped up like it should be at times. Early March the weather can be hit or miss as well. June has great weather, the folks are great and no spring breakers, or hordes of single dudes.
We always go the 3rd week of May, this year we'll be there May 16-28. We prefer May because the weather is warmer and the Memorial weekend holiday. We've been there is July. NO BUENO! Very HOT!!