I would say white.
I've always been a black iPhone guy. But with the iPhone 5, I find that there is not enough difference between the black and the slate colour, it looks rather plain in my opinion.
When I got my iPhone 5 I went for the white and silver and I really like this colouring. I think that the black iPhone 5 would have looked better with a silver back and sides (like the white one) rather than the slate colour.
