If two heroes have Keeping Count attached and they attack together, destroying an enemy do they both receive one resource token on their respective copy of Keeping Count or does the player choose who actually destroys the enemy.

For clarification, say the enemy has 1 defense and 5 health and you attack with Aragorn and Glorfindel. Do you choose that Aragorn breaks the defense, dealing 2 damage to the enemy, and Glorfindel deals 3 damage and thus would be the one who receives the resource token on Keeping Count and not Aragorn? Or are both heroes considered to have destroyed the enemy?

I believe they would both get a resource, as they have both attacked and destroyed the enemy. There are some funny rulings where you have to consider each individual character's attack strength separately (like with the Dwarf-themed tactics event Heavy Stroke), but I don't think this is one of those cases.

Yeah, they both get a resource.