Sometimes a company's biggest competitor is itself. Case in point: Toyota. Since Prius supplies are tight lately, Edmunds pitted today's most fuel efficient production car against the company's larger, hybridized Camry. While the latter doesn't achieve the same stellar numbers, the testers felt that it was a more fleshed out car. Plus, its hybrid system was more transparent in operation.

The site found that, during two weeks of testing, the Prius achieved 43.8 mpg while the Camry achieved 32.7 mpg—a savings that works out to about $40 per month over time. The two cars cost about the same, depending on options. At the same time, the Camry has a lot more room, since it's 189 inches long compared to 175 and has a longer wheelbase. They most felt it in width, though, since the car was about three to four inches wider than the Prius both outside and in.

More importantly, the Camry outdid the Prius on tech features. "Besides the standard stability control, telescopic steering wheel and the adjustable driver seat, the Camry Hybrid has other features going for it," the report said. "It also comes with dual-zone automatic climate control (with easy-to-use adjustment knobs in plain sight) and dedicated vents for the rear-seat passengers. Not so in the Prius. An auxiliary jack for an MP3 player is standard on the Camry but optional on the Prius. And the Camry Hybrid is your only choice if you want an optional sunroof."