It is quite unpredictable. Peru is on a good run, because they started with 4 points out of the first 6 games, which is a very bad start. The last three games they have won, so the momentum is there. Only problem is the play Argentina away and Colombia at home. So the schedule is pretty hard.

Argentina on the other hand, is unrecognisable, they scored a measly 16 goals in 16 matches in this qualifier, only Bolivia scored less (14 goals). With players like Messi, Di Maria, Aguero and Dybala that is unacceptable.
The schedule is in their favour, they play at home against direct competitor Peru and away against Ecuador that has lost it's last 3 games.

Hard to say, but still I go with Argentina, because of the easier schedule!