The move to E gas was prompted in large part to high levels of imported oil, the fact that corn is home grown, and its ability to boost octane number and help with emission control. One of the drives to E15 is to get more power via compression boost. The original octane booster, tetraethyl lead, is an environmental poison. I read years ago that traces of lead have been found on high mountain top water sources. The only place it could have come from was vapor from gasoline burned in vehicles. The replacement for ethyl was MTBE, but it too is an environmental pollutant when gasoline containing it leaks into the ground, not an uncommon problem.
As an octane booster and oxygenator, and having a lower pollution factor, ethanol looks to be the best choice. From the standpoint of energy output, not including the argument it takes more energy to produce it than it produces, and the impact on food supply, it is a poor choice. As in all things of life, there are no easy answers! :banghead: