Originally Posted by The Glyphstone
Okay, so I'd like to propose the following four rules for a definition of 'zombie', as I read the OP's intent:
-Must be recognizably humanoid (easy one).
-Must be capable of and required to reproduce via infection of living or dead humanoid hosts.
-Must not exceed gross physical limits of the pre-infection host body.
-Must possess an overwhelming desire to infect/kill/eat humanoids, engaging in unilateral violence whenever possible.
Well then surely the clear winner are the Trioxim Zombies from The Return of the Living Dead:
-They're exactly as physically capable as the living and are more than willing to mutilate themselves in order to reach they're prey. "And now you made me hurt myself again! You made me break my hand completely off this time Tina."
-They retain all intellect (for better or for worse) and retain they're abilities for tool use and abstract planning. (Though they do seem to gain a swarming instinct that would be detrimental vs. that can take more punishment than the normal human body.)
-They last longer and stay capable for a longer period of time. The Tarman and the Shoe Wearing Zombie were easily as strong as an animate skeleton as the other... Fuller zombies. Individual limbs are also still animate despite the lack of connection to the brain. Which is in fact unessercary to the continued survival of the undead. (Destroying the brain doesn't work.)
-They're method of infection is more effective than many others. Trioxin when introduced to the water cycle is significantly more effective (is able to leach into sealed coffins and reanimate the Shoe Wearing Zombie in minutes despite it taking several hours to turn Freddy after he was doused in the stuff) than it is in it's gaseous form and they reanimate ALL dead bodies in an area rather than requiring transfer via biting. (So if you're caught in the rain then you're screwed.)
Next comes the Marvel Zombies due to the fact that they also maintain they're physical and mental capacity but are unable to operate severed limbs from afar and are defeated by destroying the brain or severing the head.
Romero Zombies for reasons already outlined by Glyphstone.
The Shaun of the Dead Zombies. As physically capable as "core" Romero zombies but a little less intelligent. (I think we can all agree that it requires significantly more intellect to be civil than it does to play a FPS.)
28 Day's Later Zombies (Allowed because they don't enhance the infected physically they just remove the limiters that stop ourselves from hurting ourselves.) and the Solenium Zombies tie for third. They're increased aggression, speed and physical capacity bump the former up a notch but they're method for infection is incredibly inefficient and so would have lower numbers than the other zombies as well as the shorter shelf life.