The first three films have the best designs for sure. The original is about as good as a monster design can get. The Winston design has grown on me. I'm really starting to like the skull ridges and weird arm blades. The only thing that really bothers me about the dog Alien is the tail dagger is way too long.
I guess the Resurrection design doesn't bother me TOO much, but the hands are the worst. Basically this and the AVP films are where they started to get too rubbery and fleshy. Just guys in suits. They lost a lot of elegancy.
I was hoping we'd get something biomechanical and wonderful in Prometheus but instead we get Pumpkinhead Jr.