We're not talking about containment. The original discussion me and Madass were having was knowledge of the xeno and comparing the humans from the Aliens films to predators.
In Alien, they knew NOTHING about the xeno and all got easily picked apart. In aliens, they had ripley's report, which gave little more than how it was born and that its got acid blood. They didn't know about the hive, the queen or anything really. They walked straight into an ambush totally unprepared and got waxed for it. By the time they figured out tactics of the xeno, the had already lost the drop ship and the APC and most of the unit. The rest of the film consisted of them trying to escape, using salvaged weapons to survive.
The fact that the predators in the AVP franchise (regardless of the medium) hunt xeno that THEY SET UP speaks volumes about their understanding of the creature. They harvest these creatures to hunt. Their blades, armour and guns were all bigger in AVP because Anderson said they would have to be bigger to hunt xeno. Scar showed on several occasions that he knew about xenos, their weapons, the weaknesses. Bottom line is, the Preds have always shown more of an understanding than humans when it comes to xeno, and therefore would be better prepared to face them.
Oh and the xeno usually escape due to humans getting in the way and messing up the hunt. And no matter how much knowledge you have on xeno, they have a nack for escaping.