We have been through the badlands many times in the last 20+ years. Our last trip was pretty memorable. The wife is quite adamant that the "Chicken Fried Steak" we had, at the Cowboy Corner, in Interior, was the worst meal she has ever eaten, LOL. We didn't make plans, so the park's CG was full as was the KOA. We stayed at Badlands Interior motel and campground. It was pretty rough, tons of mosquitoes, and nothing special.
When it comes to CG recommendations, we really like the KOA, one of the few places with grass, shade and trees in the badlands. If you venture up to Wall, Sleepy Hollow is a real nice place. I can't say the same for the Arrow CG, which is right down the block. We typically stop at the Red Rock restaurant for a Buffalo burger when we are in town. The Wounded Knee Museum is also well worth the trip. If You're heading west to the Black Hills from the Badlands, think about staying on rt 44, instead of rt 90, it's one heck of a scenic ride. Have fun.