Mobil 1 10w 40 (not Motorcycle oil) but High Mileage. Since scooters do no have wet clutches, there is no need for m/c oils, and those friction modifies are good for your engine. Shell Rotella is a great oil also. My favorite oil is AMSOIL. It is the only TRUE "fully" synthetic oil All the rest that claim to be fully synthetic start with a crude base and as such require all sorts of additive packages to offset the harmful effects of carbon, which is found in all dino oils. AMSOIL needs no additives because it starts with an all man made synthetic base. Nothing in it comes from the ground. Unfortunately it is very hard to find on the shelf and ordering is a hassle. Everyone has his or her's favorite motor oil, but the truth is, all modern oils will get the job done id they are changed at the proper intervals. Just my thoughts.
Mac aka ole two wheels