Because of its high energy content, the same biodiesel can be used in jet aircraft as well as piston aircraft, trains, ships, boats, everything. It should be the top research direction. Hydrogen and ethanol for transportation use isn't as practical.
LNG might be, especially in a gas turbine hybrid.
"Hydrogen and ethanol for transportation use isn't as practical."
The best way to transport hydrogen is in - a hydrocarbon like gasoline. Safer, higher density, liquid so low pressure. The energy balance on ethanol is horrible.