I found an interesting article that was posted last year on USA Today, the author attempted a real world comparison of VW's diesel technology vs. Toyota's hybrid technology:

Prius is comfortable, a festival of technology and unquestionably cleaner-burning than the VW can be today with only high-sulfur diesel fuel available. But the real-world mileage of pleasant-driving Jetta was better than that of Prius, and diesel fuel typically was 16% to 20% cheaper than unleaded gas.

Jetta lived up to its one-tank billing. Prius did not.

And on top of that the only drawback that he seemed to find vis à vie the VW was environmental impact:

While the fuel price advantage on this trip goes to the diesel, the environmental advantage goes to the hybrid. The Jetta spews out six times more sulfur particulates than Prius, which can run almost emission-free when using low-sulfur gasoline available in California but almost nowhere else. Federal regulations require phasing in of low-sulfur gas and diesel the next few years, which will improve the emission performance of both gas and diesel vehicles.

[ USATODAY.com ]

Since it's been over a year from the article being written, gas prices have gone through the roof, federal guidelines about the amount of sulfur in diesel have begun to go into affect, and bio-diesel is much more prevalent than ever.