I'd say all four teams have quality enough to take it and yet a lot of issues for me to not have a definite favorite. Of course Argentina and Brazil have had major loses in the past 3 days that could affect them more. But I won't even dare to write them off.
Germany in terms of depth and overall quality have the best team left. Their defense has been suspect, and Loew tactics kinda makes one scratch their head. Portugal game aside, they haven't look too scary (I dunno, I guess that horrendous free kick vs Algeria took that scary aspect out of Germany). That said the game vs France was pretty much old Germany, to the point, effective, no need to sweat it (France helped a lot in that aspect), this is what you want from them in this matches (I felt last couple of tournaments when Germany went out in semis, they were so naive, that game vs France proved their on it). This is however, their first game against a latinamerican rival, and the home crowd effect is gonna play a role. They'll probably be up against your typical home biased ref.
Then there is Brazil, with Neymar and T.Silva out, they're the underdog in this match up, they can go to the game with a little less pressure cause if someone is to blame it will be Zuñiga. Plus they're not the team that will be to handle the offensive volume, they can play their counter attack game. The problem more than Neymar, is Silva, with Silva on, I would give the edge of this game to Brazil, without him I dont know what to make of their defense (Luiz has done good, but you know he needs a commander next to him, not sure Dante is). It's a huge loss. And then of course its their attack. In these final rounds, you want to have a good pure CF...but oh well, with Luiz and Silva in set pieces it has been enough for them in the past two games.