I'd have to go with Predator myself... He's an intelligent lifeform capable of strategy and tactics where as the Alien is just a hungry animal.. Alien kills for food...Predator kills for sport.

And if you bothered to watch Predator II, you may recall that Danny Glover discovered an Alien Skull among the Predators trophies..

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I have always been here.
I have always looked out from behind these eyes.