Alien for myself.
Predator a little too reliant on technology (and i still have major hang ups with fact they've been staging Xeno hunts for hundreds of years, have access to Xeno blood resistant materials, yet still don't fashion things like wrist blades out of said materials..).
For all the talk of code of honour. ..even with out the high tech gear, they are bigger, faster, stronger than humans, yet kill from a distance whilst cloaked far too often.
I'm drawn to the Alien because as a species it's engineered to survive in pretty much any environment it finds itself in.
Very brief maturity cycle...from chest burster to fully grown within matter of hours, it's reproductive cycle isn't restricted to trying to find a suitable mate and it takes characteristics from a host.
It's not driven by any other motive than to survive and reproduce.