Dark all the way... it's easier on my eyes than a bright white screen, it looks much more modern and sleek IMO too.
I never use the light theme, I can't stand it. In fact, I'd go as far to say that the dark theme is one of my favorite things about WP. if there weren't a dark theme I don't know that I would have even gone with Windows Phone....it would have been a much harder decision.
I've been using a dark background with teal accents, but today I switched to a white background with purple accents. Feels like I've got a new phone!
