JulesMom....was it last year that you went in March? If so, Easter was very early (March 31st) so the last week of March was part of Easter break which would have explained the huge crowds.
Easter is very late this year, so I think any time in March would be managable. Yes, the last week would be more crowded than earlier part of March because of college breaks......but no where near what last year was!!!
We went the week following Memorial Day in 98 and felt the crowds very managable!
I'm thinking both weeks would be similar in crowds for this year because of Easter being later.
Definitely a difference in temperatures though!
March can be iffy....still may be cool depending on the winter they are having. May will be hot.....and can be very hot. When we went in May....temps were recording breaking highs....90 - 95+
Even though averages are 80's.
Personnally I would choose May for the warmer temps!