...certainly not a Prius? Here is a report I read about in Car Magazine. It states that it calculated the amount of energy in producing, bringing to market, using and disposing of new vehicles in the US. The big surprise is that Hybrids are well down the list of efficient vehicles, while mechanically simple vehicles do better off.
According to the report, here are the top 5:
Dodge SX (Neon)
Here is the link: