I also vioted for Dark Sun. Here is why, for those that care.
1 - They are bringing out psionics in the next PHB. WOuld be nice to have a setting that takes full advantage of that.
2 - They don't want to get into a situation where the campaign settings start stealing players from each other. So far, FR and Eberron each occupy a specific space. They want to avoid introducing a new campaign setting that will substantially overlap with either of those two. Dragonlance, to me, is simply a variation on the "high fantasy" genre, whereas Dark Sun, from all that I have read, is fairly different in spirit (or at least previous editions were) from FR or Eberron.