I don't quite get this poll to be honest. If you already know what kind of game you are going to make, then why is it important to figure out what type of environment appeals to the most people? Look at World of Warcraft, look at Halo3, look at Oblivion or Assassin's Creed... don't they all prove that the environment really is secondary to gameplay, the kind of game and story and all that? In fact, Halo, World of Warcraft and Oblivion have a kinds of different environments... Variation is quite important me thinks.

As for my personal preferences, I'm all for sci-fi environments, but only if it's good sci-fi stuff. It's difficult to explain, but movies like Dune, Chronicles of Riddick and Firefly (Serenity) all have awesome sci-fi environments. It's a certain style though, it doesn't depend on whether the grass is green or if there's snow...