I agree with chuggs... I like the dark the best of the three, with Green being my #2...
No reason you can't give your users the choice though.
Going 100% width will give users with high screen res's a chance to view more content without scrolling, but your 800x600 users won't see the benefit, and elastic setups can mis-behave if you're not experienced in CSS...
I'm all for fixed widths
Mike.