Personally I would go for Samuel Eto'o. He's been a goal scoring machine and scored in the big games sure, but he also played with the highest intensity of any striker. He had the concept of the strikers being the first line of defense before Pep. At times he singlehandedly achieved what the front line does today. He was always underrated because people would say he only scored so many goals because he had Ronaldinho and Messi backing him up, but you can see how no other striker in the team since has been anywhere near.
David Villa was a close contender, he's been consistent and his performances for Spain have been immense. But he wasn't scoring quite as many goals as Eto'o and he didn't dominate games the same way.
Thierry Henry at Arsenal was immense at times, great goalscoring and also creating for others. On these he could have won, but he had problems at times in some big games, didn't score in either Champions League Final, and also his performances for France were nowhere near the same level.
Andriy Shevchenko, amazing player, won the Balon D'or. In terms of Talent a genuine contender. Tough one, but didn't have as many good years in the decade itself.
Zlatan Ibrahimovic, great for his club teams in many ways, but lazy so had negative affects on general play and wasn't so hot on the European and international stage.
Ruud van Nistelrooy, amazing goalscorer, but his all round play was very limited compared to the others.
