I use lucus 20w50 synthetic and it's as good as any oil I've used in the engine but my local dealer has redline vtwin synthetic for the primary so that's what I use and it's good too. Most oils are tested to a standard and it's posted on the side of the can. That makes them all very comparable quality wise, which is best?? who knows. I suggest you use the one you can get easily from a local dealer.