I prefer Badlands. Its more convenient since its right at the entrance, and you don't have to make that 15 mile trip at the beginning and end of the day. Most people consider the fact that alcohol is not allowed to be a negative, but since I'm not much of a drinker, its really not an issue for me. The big thing that Steam Corner has that Badlands is missing is shade. Its pretty much camping in a field. Also, if you don't get a reservation in early enough, you won't get a site with electricity.
All things considered, I'll be staying at Badlands.