I've taken my kids the last few years and I would highly recommend the Chula Vista resort. We always stay there; it is newer and nicer than almost any other place, has great ammenities (indoor & outdoor waterparks, several restaurants, golf course, etc). It is also less expensive than many of the big name places. The waterparks aren't as huge as some of the others, but are still very nice and we always take a day or two and leave Chula Vista to visit Mount Olympus (water park & amusement park together).
To be honest, I've stayed several places in the Dells and I don't think I'll ever stay at any other place than Chula Vista in the future.