April is a big month for spring breaks. Are there any other months you are able to travel? The first 3 weeks of May are great. Feb is a good time except around Presidents Day (the weekend around the 17th -- usually around the 14th - 20th can be pretty crowded -- I don't have a 2005 calendar in front of me).
March can be crowded, but not usually as crowded as most of April.
That said, with careful planning, you'll have a great tiem any time you go!! Hope that helps.......