It's like math. You don't believe the difference between the best and the rest until you meet the best. It is apropos that someone linked to a Terry Tao math post in this discussion, because right now, in math, Terry Tao is definitely in the "best" category. Unless we have chased the people like him away from programming, they must certainly exist in our field as well. However, our works are largely anonymous, which means that it is much harder to tell who is the best.

But Rob Pike probably is up there.