Granite Peak located in Wausau has the best park without a doubt. It's rated #1 by Transworld Snowboarding. It's got beginner parks and expert parks with very unique features.
Oh sorry I didn't see that it's in the location review section before. But I ride at granite peak too and I like their park setups too especially the shark fin that thing is sick.
With all the snow pretty much gone at the southern end of the state I am hoping to make it up and finally get to ride Granite Peak next week! Can't wait!