All right, so it may not be something to call home about, but we'll take whatever 1st place award we can get. The PS3 is the most powerful system this generation and as such, consumes the most wattage. Even the mightiest heroes cannot fight evil on an empty stomach -- bring on the feast! But first, the good news. When on standby, the PS3 is the winner on the least amount of watt usage: 0 to 1 watts are used while on standby. The Wii uses 8, and the 360 and PS2 use around 2. So, that's awesome.
What about when idle on the main menu (XMB, 360's Dashboard, the Wii's home menu)? The Wii is the clear winner, running around 15-20 watts. Second place goes to the 360, with about 145 watts. The PS3? It ranges from 185-205 watts. When running games, the numbers all go up, but the order stays the same. So there you have it -- keep the PS3 turned off if you're stepping away for a little while. Let the Wii stay on, and use your own discretion with the 360.