If you're talking about the best fuel to leave in the bike, while sitting, unused, for long periods of time, VP Hydrocarbons storage fuel blend gets my vote, followed by Trufuel, avgas and...coming in next-to-last...non-ethanol pump gas. Trufuel is sold at places like Lowes, Menard's, Home Depot...it's pricey. No gasoline is going to last forever and anything left in the carburetor is going to evaporate, leaving behind varnish. Best storage practice is to drain the entire fuel system dry...tank, lines & float bowl. If your bike has a steel fuel tank, a shot of fogging oil will prevent rust.