Excellent work Sans! I personally like the first two best, and thats mainly because the use of shadows, which definitely adds to the scene. The one i would continue working on though is number two. I think you have the best and most believable atmosphere in that one, with air that looks like it has a lot of smog, which would suit perfectly in any huge cityscape. :) I think if you tone down the haze just a little, you would bring forward the details perfectly, and all it would need really is a number of citylights in the darker areas(not too much) and some traffic further in the background Not sure i like the rays though. Better to enhance some of the highlighted areas slightly, such as the left edges of the center structure. This is all just a personal opinion though. Youre doing just fine obviously. :)

Rudolf Herczog
Digital Artist
www.rochr.com