we've heard in the past, the Wii has pretty much dominated all of the competition in each field of study. When looking at power consumption, the Wii only uses 16 watts, compared to the 119 watts of the Xbox 360 and 150 watts of the PS3.
The full NRDC study can be seen here. Warning: it's pretty much all in pdf format.
See also: Nintendo vs. Greenpeace