I like the idea of algae or bacteria to fuel. It seems to me to be the most efficient in terms of acres per litre of fuel produced.
As far as I know there are only a few more hurdles that need to be overcome before it can become an economic industry?
Biodiesel has the advantage of being able to power the current diesel engines without significant mechanical modifications. It is also a cleaner and more efficient fuel with less hazardous waste produced in its manufacture than in the case of fossil fuels.