Hybrid or diesel? For peak fuel economy in a $30,000 midsize sedan you need one or the other. The Toyota Camry is the most efficient of the five available hybrids (until the 2013 Ford Fusion arrives). If you live in Europe, the diesel world is your oyster. In North America, you have one option for an oil-burning mid-size sedan, the Volkswagen Passat. Which would you pick?