Argentina definitely had the better chances in the final before ET. Higuain went clean through early on and completely shanked it, and Messi himself put a chance he'd normally bury just wide.
The fact that it even comes down to discussing the particulars of one football match over a career that's seen him score at not much less than a game per game over 500+ games shows how preposterous the debate is.
If his team wins a particular game against, as henke says, the best team in the world, then he's the best individual player ever. If they don't win against that team, he's not. It's laughable.
This argument says that by definition, if you come from a country that's generally not very good at football, or even, say, doesn't have a good defence during a particular time period, then you can never be the best player ever. So someone comes along in five years time that is clearly better than Messi, makes Messi look bog average, wins the Champions League every year with Northampton Town and scores at a rate of 5 goals a game for 1000 games, but he's Slovakian, or Chinese, or gets injured in the WC semi final. Sorry chum. Maradona's got the trophy in the cabinet.