Which San Antonio attractions?
If you mean Sea World and the water parks, then Admiralty RV Resort on the west side of the outer loop is the best location, and a very nice park.
If you mean downtown attractions, then KOA and Traveler's World are close in and convenient to public transportation.
All of these are RV parks, the ones in town more like RV parking lots. If you really mean campground, then that would be out at Guadalupe River SP, out in Spring Branch. On the way out there, you'll see more RV parks, some of them more campground-like than those in town. There are more campgrounds on Canyon Lake, including four operated by the COE, some church camps, and a whole lot of resorts.