I voted for TDI if you convert to bio-diesel and do lots of highway traveling. I'd vote for Prius though if you do mostly in town driving.
The vote for TDI is because those motors can last 300K+ miles and if you convert to bio-diesel the operating costs would be much cheaper than the Prius (Prius having to have the battery pack replaced after roughly 5 years of service under heavy use)
EDIT: I added a poll to help visualize the votes.
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