Definitely run ethanol free, if you have access to it. As mentioned, ethanol-enriched fuel breaks down and gets stale faster, and the alcohol attracts moisture. Ethanol free produces more energy per gallon, and is easier on your engine/fuel system.
yup ethanol fuel sucks, its crap, wish more places gave you the option to NOT use it!, would save a lot of folks a lot of issues with tons of small motored things!
as for more MPG's
yes it should, as it also hold octane I am TOLD longer, so that and the ethanol making less power(slight amount)
but the gains will be SO small I doubt you would ever notice them on MPG gains
NOW on fuel lasting longer and less fuel related issue's
heck yes you will notice LESS problems from fuel over the life time of the atv
Ethanol free will make your bike run better, will not ruin your fuel pump like E10 will, and you will get better MPG.
I run ethanol free in everything but my daily driver Honda Accord. I go through a tank every week and a half in it so the E10 doesn't stay in the car long enough to screw up the fuel system. I get about 10% better MPG with ethanol free gas in the Accord, but ethanol free costs about 10-15% more than the cheap station's E10, so it's a wash on cost per mile.
Ethanol fuel sucks. Don't use it in ANY small engine if you don't have to do so.