Saturdays during the school year will definitely be the most packed, though it shouldn't be too bad. Even on crowded days in the summer you can get on all the rides several times. I've found it to be quite nice on weekends in the fall. If you can somehow manage it, they're open on Wednesdays and Thursdays in October, and the only people that make it into the park are senior citizens and a few folks with too easy jobs.