I'm certain that it will count as Aguero's goal.
I don't understand the logic of those who have said because he saved it, it is an own goal. That's even more reason why it should be Aguero's goal as if he hadn't saved it initially, the shot wouldn't have been on target.
Regardless, the precedent has been set that it will count as Aguero's goal.
Richards header v Arsenal in 2009 hit the post, hit Almunia and went in. - Here you see the shot wasn't even on target but it counted as a Richards goal.
This season, yaya's free-kick v hull was discussed by the panel and given to yaya. Though, I don't see how this ever was up for debate.