I like Predators better because they seem to have the upper hand on everything.
They are smarter then us, they developed all the technology and unless every other alien out there they don't fight for their survival, they only go to other places to hunt and to kill for their own pleasure. We only serve one purpose, prey. The whole hunting concept which combines technology and primitive, tribal aspects is very interesting.
Not to mention their great design and behaviour, which makes them really 3 dimensional characters instead of mindless killers.
Just a few out of a dozend reasons.