Well, I guess we don’t know who the winner is yet. But here are some interesting ways of trying to frame that question:

First up, the consumer payback period vs the cost of gas for your favorite alternative fuel vehicles (cars only). The only one missing is ethanol. But flex-fuel capability is super-cheap and is already included in many cars, sometimes without the owner’s knowledge, as a way to get around fuel efficiency regulations and/or capitalize on the recent ethanol fad. So paybacks are not really a barrier there.
The chart is from California’s State Alternative Fuels Plan, developed in response to AB1007 and adopted in December 2007. Actually I took it from the draft Commission-Adopted Report, because it is prettier than the final version (content unchanged). Looks like Honda’s CNG Civic is already a good deal. Fuel cells, unsurprisingly, come out as the biggest loser, with their worst-case scenario not even shown.

Next up, the global issues: energy independence and climate change. This chart is also from California’s State Alternative Fuels Plan, this time from the final version. It shows the well-to-wheels (full lifecycle) greenhouse gas and petroleum reductions achieved by each of your favorite technologies. Enjoy!