If you're interested in keeping things clean with your new E-Class, the E350 BlueTec Sedan is the way to go. At 22 mpg city and 33 mpg highway, it's the greenest of the E-Class bunch. The V-6-powered E350s range from 17/26 mpg for the Coupe to 16/23 mpg for the Wagon. Step up to the powerful V-8 and economy drop further, to 15 mpg city and 23 mpg highway for most models.
Choosing the 4Matic all-wheel-drive system instead of the standard rear-wheel drive creates a negligible penalty of 0-1 mpg on available models. Opt for the super-performance E63 AMG, however, and you'll be drinking gasoline at a rate of 13 mpg city, 20 mpg highway and 15 mpg combined--the antithesis of green.