As far as appearances go, I'd picture both as relatively normal human beings.
In my mind, I'd picture order as a businessman in the back of a crowded elevator who recieves no attention: Not just always the same person, but always viewed (or would that be ignored) in the same context.
Chaos wouldn't appear out of the ordinary until he starts to grin, at which point you notice that his teeth are massive fangs, and then when you take your attention off just the fangs to glimpse what the whole image looks like, you notice that he is twenty feet tall and in posession of thrity seven arms, and as you notice more and more, more just continues to flow forth (oh, and whatever happens to the overall shape; you can still somehow tell that he is still grinning).
There's the result of a very short brainstorm, and I must say; my image of Chaos has given me quite the appetite for breakfast.