Well this is just my personal thoughts.....i have not read the comics so i dont know what kinda detailed info they might contain, but aliens and humans appear to be the most common prey of Preds. Both are alien species so it makes sense that they would hunt each other. but according to the movies the Preds found Earth VERY far back in our history, at a time when we were archiac. So then the question has to come up of why would they start hunting us? According to their honor code, you do not hunt prey that is weaker then you. ummmmm i think an archiac race would be considered MUCH weaker then such a technically advanced one! So then why did they start?
Looking at just the Preds and Aliens, who is it that is less animalistic? Who is it that actually trains for hunting,acquires/or makes weaponry? Who is it that shows a higher intelligence as far as thinking,plotting,planning.(i mean no disrespect to the aliens i meant that as who had the most "human-like" thinking)It is the Preds!
Now you travel around to different planets and see their inhabitants. Who is it that has a closer resemblence to the Preds........Humans! Even in our archiac times,we were aleady living in organized groups, using our minds to hunt down our prey. Looking at prehistoric cultures, they carried many "trophies", amulets,etc. that carried warrior or spiritual signifisence to them. hmmmmmm Preds keep trophies, they even wear them. It hasnt really been addressed in the movies but i would wager they carry close to the same signifisence to the Preds.
So, when the Preds found us, did they find a "backwater" planet that the inhabitants needed teaching or did they find a race that had similar aspects to them. The movies showed the Preds being sent to Earth. Only the 1st movie does not show the other Preds and their ship uncloaking at the end. Did the cloaked ships in both Pred2 and AVP just sit there cloaked the entire time or is it possible that they have some sort of tracking system? If they have this then it is possible they have a way of communicating with those on the ship.
How do you learn about a people? You watch them......you hunt them. Look at the advances that we have made! Is it because we were taught by the Preds or because we possess the intelligence to evolve? I personally believe it is the latter. So i think the Preds saw in us our potential. They came here to learn about and hunt us and report of their findings. Between humans and Aliens, it is humans who have the potential to create weapons to compete with the Pred weapons. It is humans who have the potential of making many technilogical advances. Who right now is it that holds this knowledge? Preds!! So, are we a race that NEEDED to be taught by the Preds. and fell from their graces OR do we possess the capability of becoming the ULTIMATE COMPETITION?!