Zero Day
I don't understand people who try to act like either one of the boys were the leader of the army of two. I believe, like they said, there's no leader between them. They were equally toxic towards each other and encouraged each other just as much. I think this is most clear in fhe ending when Andre wants to go out and kill the cops while Cal doesn't want to do that and instead kill himself and convince Andre to. Both of them try to convince the other to do something they don't want to do and ultimately settle on Cal's plan of killing themself despite there being some hesitation on Andre's part. An occasion where Andre's will is what happens is when they steal Chris's guns. Cal wants to leave while Andre wants to stay longer to actually properly get Chris's guns and so they stay longer.
In conclusion, neither of them were the leader. They were both equally as bad for each other. If they had not met each other, the events of the movie wouldn't have happened so it was ultimately their friendship that was their doom even if their friendship was what made them happier.