With respect to Argentina, this is the squad that Don Sampa called:
Keepers - Romero (Man U), Guzman (UANL), Caballero (!) (Chelsea)
Defenders - Rojo (Man U), Funes Mori (Everton), Fazio (Roma), Otamendi (Citeh), Acuna (Sporting), Salvio (Benfica) (but who has since been taken out of the squad due to injury), Tagliafico (Ajax), Mercado (Sevilla), Bustos (Independiente)
Midfield - Mascherano (Hebei), Paredes (Zenit), Lanzini (West Ham), Lo Celso (PSG), Biglia (Milan), Banega (Sevilla), Di Maria (PSG), Perez (Boca), Meza (Independiente)
Forwards - Higuain (Juve), Messi (Barca), Aguero (Citeh), Perotti (Roma), Correa (Atleti), Pavon (Boca), Martinez (Inter as of like yesterday)
Notable omissions - Rulli (GK, Sociedad), Mammana (Zenit), Kranevitter (Zenit), Rigoni (Zenit), Pastore (PSG), Dybala (Juve), Icardi (Inter), Correa (Sevilla), Lamela (Spurs), Alario (Leverkusen)
This team is best understood from the forwards backwards. Obviously Messi is the focal point, but the traditional problem with Messi on the NT is that he is tasked with doing everything. There hasn't been a creator of enough quality to get him into advanced positions, so Messi needs to initiate the offense from a midfield that typically cannot make incisive passes. And despite having strikers of international quality (Aguero, Higuain, etc.), they still seem to have issues getting on the end of Messi's combination play. This is why I'm a bit saddened that Dybala, J. Correa, Lamela, and Alario aren't in the squad. We and Don Sampa should be familiar with what Di Maria, Higuain, and Aguero bring to the table. Dybala is the most creative and talented player that Messi has played with on the NT since Aimar/Riquelme/Crespo in 2006. I know that they tend to overlap in position a bit, but I would try and get them both on the field and build the team around BOTH of them. Dybala took a beating in the press for saying playing with Messi is hard, but I very much agree. Messi is unlike any player I've ever seen in that he sees and creates angles that no other player does and he has been in Barcelona for so long that when he is taken out of that context it requires some adjustment.
Lamela is a binky of mine as a Spurs fan, but he is also a versatile hard working player, which is incredibly valuable around WC time. J. Correa is similar. I think Higuain is probably scarred from his performances on the NT (I know I am), so I wouldn't let him anywhere near this team. Aguero has always been a beast in EPL, but his form definitely dips on NT duty. Di Maria is a good player and probably a good fit for a pressing outfit like Don Sampa envisions, but I would be more interested in giving the younger guys some run. Another couple of oldsters I've seen enough of are Banega and Biglia. Biglia is a slightly above average traditional DMF destroyer. His passing is OK and not at all incisive. UCL performances notwithstanding, I think he should be replaced by Lo Celso who has shown the mettle at PSG, but with much better forward passing. Banega has probably filled the hardest role on this squad at CMF but he hasn't excelled at it despite playing in the same role at Sevilla. He is fulcrum on which the team is balanced, so he has to pick his spots to get forward. At Sevilla, he gets more lattitude to do this and gets more opportunities. But in the conservative international game, he only gets a few chances a game and doesn't take them enough for my liking.
At the back, Otamendi is the most talented player and has done fairly well other than during Bauza's ignominious tenure. He will likely be setup in the middle alongside Masche, although Funes Mori, Fazio, and Mammana are all capable players as well. Gabi Mercado is an excellent FB, but without another on the other side, the squad lacks L/R balance. When he's on his game, Rojo is a real asset since he can play a stay at home FB or CB capably. My Man U friends hate him, but he has been solid for Argentina NT.
In net, Romero has been a rock for many many years. It's truly unfortunate IMO that he got stuck behind De Gea because he is a very solid keeper. I was surprised Rulli wasn't called since I considered him a real player for the future.
Don Sampa is a very good international manager. He took Chile's golden era of players to trophies and cohesive play. During his brief tenure so far, you can see Sampa trying to get Argentina to play his aggressive press but it's still been a work in progress. The beauty of Sampa's system is that it generates offense via turnovers in the offensive third. Thus negating Argentina's offensive weakness of getting Messi the ball in dangerous areas. Sampa has usually used a 3-3-3-1 formation and those middle 6 players will have to work a ton since Messi likely won't participate in the press and they will need to be his fellow attackers. But again, I think the key for Argentina is getting Dybala and Messi on the field at the same time without sacrificing offensive width to keep the defense honest and stretched. And since Dybala and Messi are both not deep strikers, you likely need one ahead of them.
So, a 3-4-2-1 (3-4-3) or an aggressive 4-3-2-1 (4-3-3) is what the day calls for. Let Messi and Dybala both work behind a striker. You need two midfielders on either side to provide width (take your pick among Di Maria, Lamela, A. Correa, J. Correa) and help protect the defense, and then decide whether you want one or two pivots in the midfield. In either setup, the 3 or 4 defenders are total stay at homes. Against teams with dangerous wingers, I'd go xmas tree (4-3-2-1) and against teams with more creative midfields I'd go with the Spurs special - 3-4-2-1 (again, more like 3-4-3) so that the center of the pitch gets clogged up and the ball gets forced outside.