Who's the better director? Elia Kazan or Sidney Lumet?

Both of these directors (as far as I read) have produced many classic movies throughout their career. Kazan made "A Streetcar Named Desire", "On the Waterfront", "A Face in the Crowd", and "Splendor in the Grass". Lumet (who recently died) directed "Network", "12 Angry Men", "Dog Day Afternoon", and "Prince of the City". But, who's better?