While the AT-AT has the size advantage at 74 feet tall as opposed to the Omnidroid's 50 feet, the Omnidroid outclasses the AT-AT in terms of maneuverability, armor, and weaponry. Plus, the Omnidroid's only real weakness is its own weaponry. It took five supers working together to take down the Omnidroid (which was specifically designed to kill supers), while a simple tow cable wrapped around the legs has proven more than enough to neutralize an AT-AT, which was primarily designed to transport troops. In short, the Omnidroid curbstomps. Optimus Prime (Transformers G1) vs. Leader-1 (Challenge of the GoBots). And no, anything to the effect of "OPTIMUS WINS BCUZ GOBOTS SUX LOLOLOLOLOLOL" is not an acceptable answer.