Something snowy, please! It doesn't have to be literally Antarctica - a Finnish, Icelandic, Alaskan, or Nepalese mountain village with lots of snow and ice and a few trees here and there would be fine by me, too. And I don't even care all that much about the cultural aspect of it as long as I get my eagerly awaited cold climate. We have several warm worlds, rainy worlds, and balanced worlds, what we're still missing now is a cold world.
My second choice would be Africa, especially for the cultural elements that would supposedly be very different from what we currently have in the game, but the weather could also be quite interesting, with monsoon season and all that.