Volkswagen TDIs are well-loved on the used market due to their easy drivability, the ability to modify their engines, and their excellent fuel economy. Edmunds just put that latter characteristic to the test and posted a stellar 47.3 mpg average with a 2005 Jetta, besting a 2008 Toyota Prius, a 2008 Smart ForTwo, and a 2008 Ford Focus in a set of 50 to 65 mph back road runs. It also averaged nearly 50 mpg in a 75 mph cruising test.

"If your driving is mainly around town, the Toyota Prius is a great choice—if you have the money," the report said. "If you only drive short hops and parking is tight, the Smart Fortwo is a nifty ride. The Ford Focus is another budget selection that gave us surprisingly good fuel economy on the open road. And finally, our used car contender, the 2005 VW Jetta TDI, gobbled up the open road while providing better-than-average around-town mpg."

For more analysis and a fuel economy graph showing the results, head over to GoodCleanTech.