[Khorne]

You need google more than anything else.

Ethenol based fuel is fine to put in an engine it will not corrode it. Because ethenol produces less energy than traditional fuels it requires more to be injected into the cylinder and burned so you'll use more fuel.
The octane rating is how resistent the fuel is to pre detonation, so use a higher octane if you wish to get more power, run more boost, advance timing.

Neither is better overall, each have pluses and minuses use whats best for your application.