Without question...Brad Penn. Semi synthetic, excellent product. Used it since day one, and you WILL see the difference when you pull a motor down. When your a shop like mine, you get to see a LOT of different engines. The Brad Penn engines always look great. ( obviously assuming it was built right to begin with!) we run the Nitro 70 in our Pro Top Outlaw car, and it is simply the best stuff out there. Others claim this, claim that, this stuff works.