Problem with this poll is that people see Gordon Freeman and stop. Freeman is badass for sure, but Samus Aran is inside the most powerfully advanced powered suit ever built and has earned a reputation as the most dangerous and lethal bounty hunter in the galaxy. Samus's suit makes Spartan armor look like peewee football padding. Also some people indicated that a Predator woud win, but Samus hunts things worse than him for relaxation.
Samus wins, hands down
Now if Solid Snake and Gordon Freeman teamed up with a jedi level Kyle Katarn, they might be able to take her down.... might.