"Best" depends on the criteria that you're looking at, but I like the Stanadyne Performance Formula. I run it in every fill-up all year round. I have started to run a little more than they reccomend (1.5 x) and have noticed a little more increase in fuel econ. Not suggesting you do that, just a little info on what I'm doing. We had a large shippment of it return to us due to damage, and we can't sell it, can't dump it down the drain, so I decided to run it on the heavy side in my truck.