Stalker,
Xenomorph,
17 years ago
The aliens have always been shown to be physically dominant beings, as well as the predators. They are both immensely powerful, agile, & fast. The differences between the two are weapons & skill. Aliens attack as animals...clawing, biting, stabbing with their tails. Predators have a fighting style all of their own, coupled with their brutal killing tools, it makes them more likely to come out with a victory in a 1-on-1 fight.
This, of course, is entirely down to the situation at hand. As we saw in AVP, Celtic, a relatively inexperienced predator, managed to hold off Grid with his bare hands, even overpowering & manhandling the xenomorph at times. It was quite obvious though, that should he have let his guard down, the creature would have ended his life much faster than it did. Wolf on the other hand, managed to hold off multiple aliens, even without weapons at times, which was an exaggeration to say the least. Regardless of skill or strength, not even a predator should be able to hold off two xenomorphs with its bare hands without taking some serious damage.
As far as xenomorphs as individuals go...most of the time we have seen them kill by themself, it has been through stealth. Using their natural camouflage to blend into the shadows & the surrounding environment, until they managed to get close enough to ambush their victim, in which case not even a predator would be able to defend itself...as was seen in both AVP films. They seem to be far more resourceful & intent on survival when alone...but rely more heavily on sheer numbers when the rest of their hive is on the attack.
The aliens were still very physically powerful in Requiem, as we saw one of them send Wolf flying through the air with a single strike from its tail. Unfortunately, this was one of the only scenes in the film where an individual alien actually exhibited any real intelligence or cunning...most of them just rushed at Wolf head-on, giving him more than enough time to shoot them down or prepare for a counter-attack.
The predalien on the other hand, being birthed from a predator, was even more physically powerful than The Wolf himself, & showed it by getting the better of him in several situations. In the state the creature was in, it could have very likely just had its offspring swarming through the town to quickly amass a dominant population of xenomorphs, without actually paying any real attention to the threat from the predator, which could be why the aliens were much more careless in their tactics when attacking The Wolf, as they weren't as concerned for their own survival as they were with the protection of their Queen, which could have explained their straight-forward, mindless attacks.