I almost bought a VW diesel for the consistent great mpg, but ended up with an '07 Prius. I'd say both are great options, much better than any low mpg car. The main reason I didn't by the VW diesel was seeing the many VW service complaints (check out TDIClub.com), not related to diesel technology though. I'm getting 42 mpg average on my first 2 winter tanks, 49.5 mpg on highway trips, and 75+ mpg thru the city after my car is warmed up. I expect great mpg when the weather warms up. And it's great to know my engine is shuttting off at long traffic lights and many other times seeing the car run on battery only.

Enjoy whichever high mpg car you buy, you are doing the right thing!