Mercedes S400 Image 2
The large, luxurious flagship sedan returned 29 highway mpg during our testing--a 30 percent gain over the V8-powered S550 version--and 21 mpg in the city. It achieves these numbers by combining a downsized V6 with a 20-horsepower electric motor and a 0.9 kilowatt-hour li-ion battery for a total of 295 horsepower, giving it a 0-60 time of 5.4 seconds.