In football I hate arguments that hinge on "well he hasn't won x yet". Football is a team game. You can't win if you're being used wrong, or your teammates aren't upto the standard. It doesn't matter who you are.
You could say Maradona was the best even if Messi won this WC in my opinion. People literally are just waiting on him to either win it or not win it to crown him. For me, the reason Maradona was great was because he was involved in everything the same way a Zidane was (he was the go-to guy) and had far less protection in terms of the refs, as well as scoring and making a shitload of goals. Where he loses out is in the fact that he was a liability in terms of his character. He had a shortened career because of it.
Ultimately, I think Messi's statistics are too ridiculous to argue with, when you're comparing attacking players. At 27, he's already ahead of most all-time greats in terms of their
career numbers. He is the Gretzky of our time: he is the best scorer and assister almost every year. What more, his genius makes him a devil of a player to contain, he wasn't some morde-khor like Inzaghi or Muller.
I think he should leave Barca though. He has won all he can with them. He needs a new challenge and new motivation. LIVERPOOL!