I love Longwood.
We've never been to Knoebels, though several people have told me it's fun. Mainly because it's far enough that doing a day trip seems daunting, and we are so not campers.
We did go Dorney last week (Thursday) and it was nice -- cloudy. Except when I went on that thing where you float around aimlessly on a tube in the water and my teeth started chattering because of the breeze.