I've UL91, plain EN228 unleaded (5% ethanol) and various super unleaded mogas. I notice no performance difference, but I hardly ever go above 5000 ft, so vapour pressure is not a factor for me. Avgas is ok on a limited basis, but maintenance increases as it will eventually gum up yer clutch, coat your valves etc (ul91 without any ethanol is no doubt better than mogas for the life of your fuel system)