Bonneville1
Scooter
There have been hours and hours written on this subject, general concensus is that semi synthetic is more than adequate, as for Mobil/Castrol then the Manufacturers will promote whoever ofers the best discounts, Honda I belive have moved over to Castrol? well my Honda Civic uses the stuff, As long as oil is changed at the reccomended regular intervals using the correct grade then dont worry about brand names.