I'd recommend Mobil 1, 10W-40 MX4t motorcycle oil. It's generally available at WalMart and it's good stuff. In fact, one of the Motul oils in the same viscosity has specs so similar, I suspect it's the exact same stuff at twice the price.
If you are thinking that some other oil will provide significantly longer engine life or some other such nonsense, forget it. M1, MX4t is among the best oils mankind has ever produced.
Change it regularly and enjoy your ride.