This little thing is my feelings as to why the Aliens are better than the Predators.
1. Aliens can climb on walls, whereas Predators can only hide in the trees.
2. Aliens bleed ACID, wheras Predators only bleed this green blood that doesnt do anything.
3. Aliens have an impaling tail that actually grows with them. Predators rely on blades they made to kill.
4. Aliens have all their means for killing already born with them: the tail, 2nd mouth, acid blood, etc. Predators rely on MACHINERY for their kills.
In conclusion, Aliens RULE over Predators!!!!! :D