In a universe where a Xenomorph or a Predator could be lurking behind any given cosmic corner, it seems as though one of those two incredibly deadly species would be the most threatening in the cosmos, though Aliens vs Predator proves that there is one "alien" far deadlier than either one of those intergalactic monster.
Both Alien’s Xenomorphs and Predator’s titular space hunter got their start in film with each of them violently existing in separate universes. The two aliens didn’t share the stage until Dark Horse Comics’ 1989 comic series Aliens vs Predator hit the shelves, sparking an immensely popular decades-long franchise. In fact, the two species became so intertwined that within the established AvP universe of Dark Horse Comics, it was revealed that Xenomorphs actually play a key role in Predator development as each hunter has to kill one of the serpent-like beasts before being considered a respectable member of the tribe. This also explained how Xenomorphs kept popping up on random planets despite the fact that they are incapable of interplanetary travel as Predators systematically kidnap Queen Aliens from existing hives and move them to another location, further expanding their hunting grounds. As surprising as it may seem, however, Xenomorphs and Predators aren’t actually the greatest danger to the planets they visit as that title is held by another species all together.
In Aliens vs Predator #0 by Randy Stradley and Phill Norwood, readers are thrown right into the further reaches of space as a mining colony is traveling through the stars on their way to drop off the latest shipment of resources collected from far off worlds. In these opening pages, there is a conversation between two workers, Tom and Scott, who are discussing the morality of their line of work as well as that of humanity’s dependance the stolen resources they ship. Tom thinks it is wrong that humans think they can invade far off planets within the AvP universe, drain them of all their worth, and leave having irrevocably changed that planet’s habitat for the worse. Scott is in complete disagreement, arguing that humans have every right to keep going the way they are since they have the means to do so and because there aren’t many other options available to them since it seems Earth has been tapped dry. The truth is, however, that their conversation–while enlightening–makes no difference on the current state of humanity in that world as humans will continue to drain life from other planets so long as it is profitable.
Through this simple exchange alone, without the need to delve into the histories or impacts of Predators and Xenomorphs, makes it clear that humans are the deadliest species in the cosmos. Predators leave little to no impact on the worlds they visit aside from hunting the indigenous life there, and Xenomorphs can only go where they are brought which isn’t nearly as expansive as humanity’s reach at this point in AvP continuity. Humans, on the other hand, systematically make entire worlds unlivable, and no amount of Xenomorph or Predator attacks have slowed that process throughout the franchise.
While it could be argued that Xenomorphs ravage the worlds they inhabit, they don’t actively seek out worlds to destroy for their own personal gain, they are simply brought to a planet by the Predators and exist there. Humans knowingly wipe out entire alien ecosystems and do so at a much greater rate than Xenomorphs, which is proven true by the fact that many space-traveling humans don’t even know Xenomorphs exist. Humans have become the conquering aliens to these other worlds, and their method of draining them of all their resources has become terrifyingly efficient–proving that within the world of Aliens vs Predator, humans are an even deadlier ‘alien’ species than Xenomorphs and Predators.