We live just a few hours from the dells and have pretty much been to all of the Dells waterparks, indoors and out at different times of the year. We do a lot of 3 day get aways there since its cost effective and fun.
Hands down our favorite place to stay is the Kalahari. They have a very large indoor dry theme park, a great indoor water park and excellent outdoor waterpark.
Reasons I like it over Great Wolf Lodge:
1. Water is warmer. W/ a two year old that was huge for me. I was freezing at Great Wolf.
2. Better food. Kalahari is themed very well.. I can order healthy food, salads, panini's, wraps and it has more choices for resteraunts. At Great wolf we were only able to find pizza and one resteraunt, which was very slow. Kalahari also has an awesome sweet treats stand, to die for!
If you do book though make sure to ask to stay in the main building, its a very far walk to the far building. Last time we stayed we got a two bedroom on the first floor off the walkway to the indoor theme park. It had an outdoor patio with patio table and chairs. It was awesome because while our toddler was napping in the room we were able to sit on the patio in the sun and read while watching our older son in the waterpark.