if you're running a basic engine, with little in the way of mods, either E85 (ethanol blend 85RON fuel) or standard unleaded (91RON) will be fine...
these engines, unless you've bumped the compression up and dicked with the ignition advance, arent really capable of compressing and burning high octane fuel properly...
you will probably notice the best burn from E85...
that will set the cat amongst the pigeons no doubt, but that's just my experience...
i've tried everything from 91 octane standard pump unleaded to Elf race fuels to avgas with an octane booster (bout 101RON) and standard shitty pump fuel ran cleanest...
low compression low revving motors with mild ignition advance dont need much in the way of quality fuel...