That means you can enjoy the films in almost any order you want, but the best way to watch them is still the order in which they were released. As a fan, you not only get a number of Easter eggs (things that happen in "Predator" are heavily referenced in "Predators," for example), but you also get to see the visual, stylistic, and narrative evolution of a movie franchise. 

The pacing of a movie like "Prey" is deliberately referencing the way the climax of "Predator" comes about, while "The Predator" is full of knowing winks to the franchise's larger history. Watching the films in the order that they were made ensures that you notice all of these winks and nods to what came before, and gives you a more fully-formed appreciation of the larger franchise.