I think the Alien is more interesting to think about if it's a thinking sadistic bastard. The Aliens in the latter movies follow the more survival traits, but the first Alien definitely has a menace to him which is more interesting to me personally. I wouldn't necessarily say "evil" is the right word to describe him, but I like to think of it like a being without any moral boundaries or dilemmas, so it would be free to indulge in what it desires at any given time with no after-thought. I think that makes the Alien more frightening.