Best looking concept that I've seen on the forum so far. I like the top Right. Bottom right looks cool, but I always prefer hot looking environments to icy cold ones.
After giving it some thought I think a combination of the elements would look best. Top left has the best foreground elements, bottom left the most interesting building silhouette, and bottom right the best color contrast, while I think the top right has the darkest mood.
The bottom right one is definitely my favorite. The cool blues from the ice chasms juxtaposed with the orange from the structures are a lot more visually interesting to me than the others which just look like standard desert/refinery. Plus I think an ice chasm like that would provide a lot of opportunities with gameplay.