When are you going? The time of year does make a difference in crowds and available campgrounds. We stayed at the Sylvan Lake CG at Custer and had to get reservations even in mid-September. The problem was that the sites were VERY close together, a long way from the lake, and the nearest CSP dump station was more than 20 miles away. We won't stay at any of the CSP campgrounds again--would rather pay a little more (not much with the daily pass added) and stay in a private RV park.
We also didn't think much of the Wind Cave NP campground. Again too closely spaced, no privacy, and no hookups.
However, we loved our hilltop campsite with hookups and a great view at Angostura Lake State Recreation Area SE of Hot Springs. A longer drive, but well worth it for the amenities, including a new, clean shower building, big spaces, and lack of crowds. We would go back there in a minute!
