Predator has 'feelings' doesn't it? I think I remember seeing it get all 'fuzzy' before...
Fatal flaw.
Alien has an insect's survival instinct, not confusing & cerebral like Pred.

Quote from Alien (not exact) regarding acid blood... "It has a great defense mechanism... Don't dare kill it."

No doubt in my mind.
Like RJjr vs Tarver... oh wait, never mind...