It's a hard choice, considering that they are both so differently awesome in so many different ways, but in the end I've always liked the Alien series like .01% more, and I always find myself saying, "come on man, kill him, kill him, use your tounge, go through his head, please, pretty please, WHAT, you got killed, you had the guys foot, and some retard turned upside down and started shooting at you and just blew your head up, AHHHHHHHHHHH, what the F*ck, AHHHHHHHHHHHH!
So yeah, Alien. Design looks cooler, seems to have an interesting lifestyle.