2012 Mercedes S-Class S 65 AMG

Efficiency-minded buyers have their pick of hybrid or diesel with the S-class. The turbo-diesel V-6 is projected to earn a rating of 20/31 mpg on the EPA fuel economy cycle and is both refined and authoritative, but it is slow to respond off the line and during downshifts. Accordingly, we're not as impressed with the new engine as we have been with the less powerful Mercedes diesel or the diesels offered by BMW and Audi. For now, though, Mercedes is the only company to offer a diesel in a flagship luxury sedan. The S400 Hybrid was the first gas/electric car to use lithium-ion batteries and delivers impressive fuel economy and smooth acceleration from its V-6 engine and electric motor, but at 19/25 mpg it isn't as efficient as the diesel. The rest of the lineup focuses on speed, not economy. The S550 is powered by a 4.7-liter twin-turbo V-8 and accelerates to 60 mph in 5.4 seconds. Next up the food chain is the 510-hp S600 supersedan with a twin-turbo V-12 engine that accomplishes the same task in a paltry 4.5 seconds. Then there's the 536-hp S63 AMG with the twin-turbocharged 5.5-liter V-8 that has replaced the 6.2-liter normally aspirated V-8. All those luxorockets, however, are left behind by the ludicrously fast S65 AMG and its twin-turbo V-12 that makes 621 hp and a massive 738 lb-ft of torque. But the S-class is more than great engines; it's also a driver's delight thanks to a balanced chassis, superb steering, and a supple ride.