No key? Strikes if you are with a team that is willing to speed run them. Go as fast as you can, you can probably knock out 2 for every one POE, maybe 3 if the right playlists come up.
However, that's really just engrams, and the possible legendary gun.
The POE also gives you the side chests, and a shot at a key for a better reward.
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I think PoE would give more rewards. But it's a toss up for exotic weapons.