I go up to Kohler about two times a year to play. That being said, I've never played, but heard wonderful things about, the Bull. It is a Nickalus design. If you are looking for another track, I would suggest giving it a whirl....and then let us know how it is.
If you want to stay in Kohler proper though, you can't go wrong with any of the resort 4. I, for one, like the back nine of the Meadows more than either nine of the River. However, from 1 to 18, the River is a better course.
Have fun though, you'll love it.