Definitely a must when in Chi, but imo Art of Pizza was just on a completely different level.
One thing that bothers me about Lou's, although I can't really put my finger on it, is that their flash frozen pizzas you can buy online are almost as good as the real thing if you cook them right. That's actually a good thing, but something about it just doesn't seem right, you know? Like eating the real thing in the restaurant should totally blow away the home version, except...it doesn't.
Whatever. Great pizzas both, and the pizza wars of Chicago will rage as long as the city is around.