Mobil 1 10-40 Motorcycle Oil works well too, its a little on the expensive side $8.19/qt at AAP but holds up well. In a prior post I have heard it works well as gear oil too, I am anxious to give that combo a try this spring/summer.
If that scooter is air-cooled, I would be using a good 20/50 or 15/50. Those little fellas are working hard all the time and get red hot. Synthetic would be best but even a dino would give you good service.
Synthetic should be cosiderably better in that application. You are operating an engine that size flat out most of the time.You need all the protection you can get.