Currently i like C2 with the light UI (grey background and black text). Some of people request for next update C3 with black background and white text (and i think oh my god... please don't do it ashley)
Personally I don't like a completely black background with white text, it physically hurts my eyes and gives very bad ghosting. If you take a look on the newer unity release (4.5 and later) they change background from black to grey with the black text because they're understand light background was much better than the new white text on black background.