I'll have to agree that the answer is not clear because of the muddled attack vs attack power debacle.
However, from Hunter's Quarry:
"If you can make multiple attacks in a round, you decide which attack to apply the extra damage to after all the attacks are rolled."
From this snippet, I glean that you make the attacks first, decide which attack gets your quarry damage, then roll damage. This way you are making sure if either one of the attacks is a critical hit, you can apply the damage to that hit. So theoretically, you don't even know if an attack would drop a target or not until both attack rolls have been resolved.
I think the intent is that you pick the targets, roll the attacks, then roll the damage.
Having said that, as a house rule, I completely ignore the snippet I quoted, for no other reason than to speed up resolution. I don't need the ranger pondering on his turn whether he should pick one target or two targets (players get pondersome enough as it is). The freedom to make the first attack and the damage roll makes decisions easier. Of course you lose the flexibility to gain maximum benefit from critical hits when you are resolving damage before the second attack. But you get the benefit of taking a shot at a different target when the first goes down, or targeting the same target if you miss. I just find this is a speedier way to resolve things.