What I use in mine (Yamaha, Honda, Chinese, etc.) is Rotella T 15w40 - or maybe T6 (5w40) in cold weather. It's hard to beat the price/quality mark with HDEO's. Since most scooters have a CVT, they continuously run high rpm's and need all of the protection they can get - more so if yours is air-cooled.
Of course, i've recently stocked up on DELO since many Wal-marts have it on Rollback for $8.50/gallon. Hard to go wrong at that price and a great oil to boot.