
Ah, the age old question, who is the best poker player? To sort through this quandary we should first decide what makes someone the best.
Measuring someones poker ability is done in 1 simple way: money! Normally how much money a player has won is in direct correlation with his ability. However, there are exceptions. Take Jamie Gold for example: Gold won the 2006 WSOP, and $12,000,000, but no one would call him a top player, let alone the best player in the world!
So not only do we have to look at the amount of money they have won, but also how they won it. A single lucky score cannot count, much like a player called up from the minors who cranks a homer in his one and only at bat isn't considered the most prolific slugger in baseball! There has to be some longevity to their career.
The final characteristic I would look at would be the respect they garner from their peers. A player like Johnny Moss, who cut his teeth when the game was still played in backrooms of poolhalls, didn't have the same opportunities that exist today. Yet many would list him as the greatest poker player of all time despite the fact his career winnings would be considered low by todays standards.

So, to answer our original question; it depends! It depends not only on the criteria I have outlined, but also if you are talking tournaments or cash games, Texas Hold' Em or Pot Limit Omaha, or simply best all-around player.
Since I dodged my own question I'll give you some of my opinions on who the best players are:
Best all-around player - The late Chip Reese with an honorable mention to Daniel Negraneau, Phil Ivey, and Doyle Brunson.
Best Tournament player - There are many: Daniel, Phil Helmuth, Mike "The Grinder" Mizrachi, but for my money it's the late Stu Ungar. If you've never heard of Stuey go pick up a copy of Nolan Dalla's biography of him.
Best cash game players - David Benyamine, Patrik Antonius, Jen Harmon, there are just so many great players you could argue until the cows come home.

So, who is the best player? I'll leave that up to you the reader to decide. Feel free to argue about any of my choices, or elevate one of your own, by leaving a comment.