CG to me suits the aliens better because of there frame. Humans are still humans even in suits, so a human can never fully act or pose like a alien without it looking like a guy in a rubber suit. Why do you think they always did close ups back in the days? never actually showing the full body? as an alien walks? it's just impossible to do without CG.
This is what an alien looks like for the most part. Maby some changes to the head and body. But the basic shape of a full body alien is this. A guy in a rubber suit could never do that. The Alien in AR in that breif scene walked like this one is standing. So it's consistant. Sure a guy in a suit could do the top half on closeups. And im fine with that. Nothing beats the creature actually being on screen with the actors, than some CG thing added later. I just hope in the prequel we get more shots of the creature actually walking or running.