I use the Mobil 1 synthetic 20/50 for V-Twins. As an aside I would also agree that changing the oil out religiously is probably more important than the oil itself.
With the average annual mileage we do coupled with the at least yearly oil changes it truly doesn't matter which oil you use as long as it is a 20/50 V-Twin oil.
I agree that that's the case for a water-cooled engine, but per JMD's above post, not for an air-cooled one.
