Say the world champion could play heads up against any player and in the long run come out ahead. That would seem to be one good way to describe a champion.

Although it may skew the champion to one that plays well heads up. Perhaps another way to determine the champion is the one who earns the most money, but that may take into account other things rather than pure poker playing like table selection, amount time played.

I like the idea that the champion could generally outplay anyone else over a long period of time.