I love both, but my favorite are the Predators. The original Predator is what I watched first, often with my father. Alien came a little later.
I remember being very upset back in 2004 (I was 14 then) when Grid killed both Chopper and Celtic in a row
I was like "Hell yeah, 3 Predators! There's going to be a lot of cool fights against the Aliens and... wait a minute... what?!"