What is best alternative fuel source?

In the pageant of competing clean fuel, synthetic fuels come in last place. Although only slightly better than fossil fuels, they may work as a transition fuel since they can be blended with gas or diesel to produce lower levels of pollutants. With gas pipelines already in the ground, another transition fuel is natural gas. Both natural gas and Liquid Petroleum Gas (LPG) produce fewer emissions and are clean-burning fuels that don't threaten soils or ground or surface water. Biogas is another semi-clean fuel that can be blended with hydrogen to create fewer emissions. Ultra-low Sulfur Diesel (ULSD) can be blended with biodiesel to reduce emissions, but burning 100% biodiesel may release excess nitrogen oxides, and fossil fuels are used in the production process.