Predator would win.
Simple as that, no questions asked!
Aliens are pretty much designed to be hunted an raped by Predators.
They're pretty much animals that only have 1 instinct: kill.
Ya sure sounds bad ass, but compared to a Predator the Alien is just some unintellient animal. Predators have a complete civilization, and you know, they arent born by ripping out of someones chest.