Brazil is every time favorite because they have good record in World Cup Matches but we can watch some good underdogs as well because now time is changing very quickly and many teams can give shock to these bigs
There are quite a few underdogs, who can give big shock to the favorites. Belgium is one of such underdogs. Others that come to my mind right now are Colombia, Uruguay, and Croatia.
IMO, Croatia isn't an underdog. They qualified to the WC by playing the playoffs, in one of their recent friendlies they lost against Peru (an inferior team), they only have two or three top players, the rest are just average...overall, it's very hard to put Croatia among the underdogs when they're clearly inferior to such underdogs.
About Belgium, i'm having a
déjà vu when people mention Belgium, same thing happened in the WC 2014 and Euro 2016 and both times they were a complete dissapointment.
true Croatia is in first tier right now, maybe 2nd behind Germany, France and Spain and in their group Iceland is a very physical team they can be a surprise again. And for Argentina i really still can't figure out what they're going to do the team have the best player and a of the best strikers so in my opinion group D looks the toughest group because the level is close between the teams while the others groups have one or two weak teams that's why I think group E is the weaker group Brazil is far superior team then the rest and it will be though to see who will join them in 2nd place.