Which water park over spring break?

[Tinker Mel]

My 11 and 13 yo girls really want to do a water park while we are at Disney 4/7-11. I am thinking Monday, the 10th but am wondering which park. They are not into ultimate thrill rides; just a fun day with a "tropical" or beach atmosphere. Which park do you recommend? Should we go first thing in am or later in the day? I am worried about it reaching capacity around noon and not being able to get in.