Pros: Open 24 hours, underground parking.
Cons: Always busy. Often picked over. It's a Walmart.
The worst Madison area Walmart is the west one. NOT open 24 hours, small, often out of stock, often a mess, and there's ALWAYS a line at customer service no matter when you go. One of the staff members I frequently encounter at customer service is rude.
Sun Prairie and Stoughton are tied for best. More likely to be in stock. More likely to be clean. Never had an issue with the staff. Open 24 hours. Probably helps that they are further from Madison proper and therefore less trafficed.
Madison East (Nakoosa Trail) would be similar except it's not 24 hours.