#4 Lionel Messi

Admittedly, Messi should be further higher on this list, but after the way Argentina qualified for the World Cup, it is fair to put him in the fourth position.
Make no mistake, Argentina are more than capable of winning this tournament under Sampaoli. But they have a history of choking under pressure, and they are yet to gel as a team, unlike Germany or Brazil.
In the last few years, Messi has moved from a position of striker to more and more as a central midfielder who makes things happen, instead of roaming the opposition box looking for a stray pass. With Aguero (and not Higuain) and Dybala, that will be more to Argentina's strengths.
Despite all this, he has managed to score 44 goals for Barcelona this season and is in white-hot form. He could very well win the Golden Boot, but it will depend a lot on how his teammates play as well. Knowing Argentina, that is asking a lot.