Butanol can be used at 85% with no modifications to engines, has more power than ethanol, and can be produced from biomass. So, the head of DuPont says, this is what cars should run on. Sure, DuPont would be happy to produce it in massive quantities, but he does have a point. We must replace petroleum-based fuel with something else.
For the first decade or two of the switch-over to clean energy, vehicles will probably be powered a number of ways, like electricity, hydrogen, and biofuel. Then a few dominant technologies will emerge. This is what happened during 1890-1910 or so, when there were steam, electric, and gas vehicles on the road, and no clear winner.