To my mind, the "best wonder" depends on how you play civilization. My way is building many big cities with cathedrals in all of them. Then, when i got ~20 cities with 40 shields-production in each, i launch SS, or mass-produced bombers, carriers and armors. With such a civilization, i think Michelangelo's chapel is the most profitable wonder: 4 unhappy changed in content, each turn, in each cities (with cathedral), till the end of the game - the end, as i never discover communism, and never give the other civs the time to discover it. 
