Butanol before ethanol, and biodiesel before either of them, in my opinion. I think hydrogen could be made viable, though. Remember, gasoline wasn’t viable when all we had was whale oil.
There has already been a lot of government money toward making hydrogen "viable". California had a heavily subsidized program, but even with huge tax credits, they couldn't make it viable. The last few stations shut down a few months ago. I think it's naive to think that throwing money at technologies will make them viable.
If you study the history of natural resources use; whale oil was expensive, and kerosene came onto the market as a cheaper, and better alternative, all without government funded anything. This could happen again, if governm,et would get the heck out of the way with all it's crippling regulations.
Coal gasification is already being used in China, and would likely be the most viable ( meaning : cheaper) alternative, if we could just build the damn plants.
You can thank the Environmental Defense Fund lawyers for that - they assign a lawyer to every coal plant that comes up for permitting, with the sole purpose of shutting it down.
Algae might look good on paper, but is decades away from anything even remotely practical.