Well I use M1 because its easy to find, cheap, reputable brand, dont have to pay for shipping. I would use amsoil if it was close in price but I think last time i checked it was close to $50 for a gallon and a quart or two on the side plus shipping.
Does anyone have any cheap sources? or coupon codes for it?
AND i forget where i read but that the OE is very similair to M1 and both are group III i think. I think the XL and signature are group 4? I may be wrong about this.