Do you like the concept of Preserving or Defiling better?
I have to go with Defiling. Really, that's how Dark Sun got to be a desert. Once again, I had very little true knowledge of the pulp classics like Conan or Fafhrd and the Grey Mouser. However, something about the drawback to magic use made sense to me. I instinctively knew magic use was dangerous and now I had a mechanic for it. It also gave a dichotomy to magic users, who I always felt were too carbon-copy. Would I have ever played one? I don't know; I never was big on magic users in general. It would have been interesting; unfortunately, I was the DD: Designated Dungeonmaster. :)