I like ATW, and I've rent a car there before without problem. The airport is small, but close to the Interstate, they have enough flights and carriers, that if you have irregular ops, you'll still get to where you are going. They have a small gift shop, lunch counter, and a small Wisconsin Cheese shop.

If you do fly in, I would highly recommend you visit http://museum.eaa.org/ in near by Oshkosh, WI.

I would also consider MKE as the drive from MKE to GRB isn't much further than the drive from ATW to GRB. Also factor in your rental car costs, as the cost of a rental in MKE might be lower than in ATW.