Within the established Alien universe, it is basically a known fact that the Xenomorph is the deadliest creature in the cosmos, as it has been quite literally described as the perfect organism. However, while on a mission unrelated to the Xenomorph species, a team of Colonial Marines actually encounter an alien that they determine is far deadlier.

The first time the wider human species encountered the Xenomorphs was in the film Aliens. While the crew of the Nostromo came across one in the first Alien movie, the aliens weren’t cataloged until the sequel. While Weyland-Yutani assuredly did everything they could to cover up the aliens' existence after Aliens’ Colonial Marines. This means that the Colonial Marines who took up arms after the group from Aliens must have been made aware of the Xenomorphs, and were given the training necessary to combat them. So, every alien life form encountered by the Colonial Marines were immediately held up to the standard set by the Xenomorphs–and there’s one in particular that sured that particular standard: the Predators.

Predators are Deadlier than Xenomorphs, & the Colonial Marines Prove it

In Predator: Life and Death #4 by Dan Abnett and Brian Albert Thies, a team of Colonial Marines were working in conjunction with Weyland-Yutani to ensure that a world that was legally claimed by the company was physically secured without issue. Unfortunately, this world was crawling with Predators who were there to hunt the indigenous life forms before humans found themselves in the middle of their hunt. In this issue (which is the final one in the miniseries) the Colonial Marines are having their last stand against the Predators, at which point one of the commanding officers names the ‘Hunters’ aka the Predators as the deadliest creatures that the corp has ever faced, and that this battle will be taught in future training courses.

The fact that a high ranking officer said this about the Predators means that the Yautja are definitely more dangerous to humans than Xenomorphs. This story takes place nearly fifty years after the events of Aliens, so anti-Xenomorph training would have been implemented for decades, assuming the Colonial Marines knew about the Xenomorphs themselves (as previously established). So, it is safe to assume that this officer is well aware of Xenomorphs, knows exactly how deadly they are, and trained her team on how to battle them, and she says that Predators are the deadliest creatures she or the entirety of the Colonial Marines ever encountered.

This is an interesting development since Predators are named even deadlier than Xenomorphs without the two creatures ever coming into with one another. While the Life and Death storyline is an Alien vs Predator story, this miniseries within the wider narrative only deals with Predators vs Colonial Marines. So, in this case, it was the implied comparison on the part of the Colonial Marines that determined Predators are the deadliest species in the cosmos, not Alien’s Xenomorphs–and in a way, that third-party perspective is even more valuable.