Probably several opinions on what is best, brands like Redline and LE oils can run as high as $15 dollars a quart and they are really good or you can go to the local discount auto and buy Castrol/Quaker State etc. for $3 dollars a quart. See if anyone else chimes in. Cost, quality, volume of potential leaks in the future may determine what you want to use. I used a brand called Lucas which was sort of mid-point priced $6 I think. I figured since I probably won't change it that often I would use something heavy duty and I had used their products before.
