Alien vs. Predator
itself is designed like the ultimate in rock, paper, scissors. Humans are the ultimate armored machine. They use motion trackers, heavy armor, and more ammunition than you can shake a stick at.
Predators of course are the ultimate sniper. They are created to hit and run one opponent at a time. Most of their weapons are designed for one shot, one kill, and they receive no upgrades.
Aliens are the ultimate in pack hunting and close combat. In groups, even the most experienced of marines will have trouble, and predators might as well not waste their energy trying to cloak from the armored wolves.