I resist declaring any one or other as "the greatest", strictly because the criteria for such a declaration will change with the viewer. However, Geiger's ALIEN certainly deserves a high place in the pantheon of movie creatures. Besides being a work of art for its much-copied design, it was a deeply, viscerally frightening monster, bringing all manner of psychological fears with it out of the shadows due to its well-thought out life cycle and story. Bottom line, few movie monsters "git 'er dun" (that is, scare the beejabbers out of the audience) like the Alien.
Godzilla is a "Git 'er Dun" monster as well, but his intention is NOT to frighten people right down to their innermost core. His role in his films is more to evoke a sense of awe and admiration (and, of course, catharsis...who among his fans has never fantasized, even once, of what it would be like to wield his overwhelming power? To run as wild with it as he does?). He does what he does by his nature, as sureley as the Alien does, but his is the more lighter, kid-friendly path. Godzilla might attack our cities, but he does not haunt our nightmares.
Thus, comparing him to Geiger's ALIEN is somewhat unfair. The ALIEN was masterfully designed to lurk in our dark places, around deserted corners and in murky rooms, filling us with fear before its presence is even known. It lives in the dark, in our worst childhood fears of the boogeyman, and in our most dire adult fears of rape and penetration.
Godzilla, even when he is most perfectly presented and filmed, even if someday he is realized with perfect realism onscreen, is NOT a lurking, creeping terror in the shadows, nor was he ever intended to be. Originally, he was a cautionary metaphor for nuclear weapons; inspired by the worst nuclear accident in US history (Google the words CASTLE BRAVO to read about this). Later, he morphed into a defender of the Earth, and finally into a simple animal; a creature beyond all control and motivation save territoriality and defense of his young - a natural force like a hurricane, showing humans how truly small we were next to nature's wrath.
Two monsters here; both completely different to the point of being incomparable to each other, but both so startlingly effective in their presentation as to become icons.
You've good taste in monsters, Sir!
Thanks you very much. I'm a huge fan of the ALIEN. I love the way it looks. I'm a huge fan of Godzilla too. You can ask my Mom, 'visualops', to verify it. When I was little I watch every still movie and had tons of Godzilla toys.