Since the can of worms is already opened...
Just my $.02 I used to use Royal Purple in any two wheeled vehicle I owned. Recently I have converted to diesel oil ( either Mobil Delvac, Shell Rotella etc. ) On both my Max and Wife's Kawasaki Dual Sport.
Not only are diesel oils inexpensive, they also come in 15-40 which is tight in the viscosity range everyone mentioned above but they also have higher zinc content ( like a bike specific oil ) which is beneficial to wet clutches.
I would say rather than what oil TO use it is more important to know what NOT to use. Whether you go Dino or full synthetic, car, bike, diesel specific, top shelf or bargain avoid one thing: If the oil has the " energy conserving " starburst symbol on the back do not put it in a bike. It will hasten the demise of your clutch plates.