Personally I run the HP Ultra oil, and for me it is actually cheaper than Amsoil will ever be. My dealer has given me a free 6 pack of 2 gal mixes, as well as giving me a discount on all others I got. In my opinion, if Stihl is willing to DOUBLE the warranty, the oil has to be good.
If it ain't orange and white then it ain't right!
Honda HRC216HXA Commercial 21" Mower
Stihl KM110 with String Trimmer, Articulating Hedge Trimmer, and Pick Tine Cultivator
Stihl BR600 Backpack Blower
Stihl SH56 Shredder Vac
Stihl MS250 Chain Saw