Six Flags Great Adventure is better than Lagoon (thought I'd include a park few people on here have been to) but not as good as Knoebels.
Lagoon has a great lineup of coasters, but lacks a signature ride. Although, when Canibal opens in 2015 they will have their signature coaster. They also have a ton of flat rides... A top scan, S&S towers, Air race, plus all the classics. The atmosphere of the place is also great.
Knoebels is the perfect park, no park is better.
Knoebels has great rides, great staff, great food, a great atmosphere, a nice, scenic location... I could go on and on.