Which is better - 90 octane no ethanol or 93 octane 10% ethanol

It depends on if you need the octane and alcohol or not. I like the the 93 ethanol fuel. My 500ci motor diesels horribly when shutting it off hot with 91 non eth fuel but does not with 93 eth. I agree that the ethanol fuels do go bad faster and clog up and fuel system but that is preventable with additves in the off season.