I voted "pretty much the same".
I've gone in late April/early May for the past 3 years (this will be my 4th).
2004 - went end of April
2005 - 1st week of May
2006 - 2nd week of May
In April, the crowds were a little bit lower..but the weather was cooler.
In May, slightly bigger crowds, ....but warmer temps.
We stayed for 9 days each trip & it only rained once each time! Unbelievable!!