Fuels comprised of shorter hydrocarbon chains carry more of their energy as Hydrogen. The ratio of H/C goes up as the length goes down.
As others have pointed out, biofuels are derived from the current rather than prehistoric carbon cycles. Unfortunately the world appetite for energy has the capacity to completely overwhelm the natural carbon cycle. We would have to denude the planet several times over on a regular basis in order to replace fossil fuels.
Another point missed is that transferring combustion of Carbon to combustion of Hydrogen is a completely wrong approach if you buy into the opinion that significant anthropogenic global warming is occurring. Water vaporor is a more powerful greenhouse gas than CO2.
With that said, I like biofuels, I'd like to see or create an enabling technology that will allow individuals to exploit various niche sources as they may be available.
Couple quickies --
(1) the (substantial) energy stored in the hydrogen bonds of short-chain hydrocarbon fuels is not available to use as fuel energy; and
(2) instead of denuding the earth to produce biofuels, (which they would) AND consuming ABSURD amounts of 'fresh' water, we should look at aquatic chlorophyta (green plants that grow in the oceans-- plankton, kelp, Ulva lactuca, usw) as a means to capture carbon.
Just to really scare the greenies ... We could use NUCLEAR POWER plants to 'sterilize' municipal sewage; use the sewage as the nitrogen and phosphorous source the phytoplankton would love; use the waste heat from the reactors to drive the fermentation (or other process), and use the biomass of the phytoplankton to produce methane and fertilizer. Oh, the phytoplankton are also naturally pretty good heavy metal sinks as well, ( not as good as water hyacinths ) so we could clean up the sewage as we turn it (and sunlight and CO2) into fuel.
OK, kevlar now on ...