I would have to go with the 7.62x39.
The 5.56 beats it on range, but most fighting now days is city, door to door.
I have a buddy who, while serving in Iraq, shot an insurgent. he hit the guy in the chest. He said the guy didn't even flinch, he just dropped his gun and asked to be taken for medical aid.
The 7.62 round would have put the insurgent down and out.
So for up close, put down power, go with the 7.62.