Yeah car of the decade could probably belong to a Honda in the 90s but to many companies like Nissan, Hyundai, and VW have put out some vast improvements compared to the last decade. As far as most improved I'd have to say Hyundai.

My vote for best car of the decade would go to either the veyron or prius. Best car has nothing to do with best value. It comes down what kind of a driver are you? This will be bias no matter what.