Easily Cybermen, they defeat all the other armies combined with ease:
Stormtroopers, legendary for being pathetic, lost to Ewoks.
Koopa Troopas, shells won't do much to Cybermen.
Orcs, Pre-Gunpowder weapons will be ineffective against Cybermen.
Zombies, Bites won't penetrate the metal outer casing.
Roman Army, like with Orcs, Pre-Gunpowder weapons won't do much.
Skynet, was losing to the remnants of early 21st Century humanity, Terminators were meant to turn the tide. Cybermen are far more numerous and technologically advanced.
The Martians, were killed by microbes, Cybermen can easily engineer a virus, and their Walkers don't compare to Cyberships.
So yeah, Cybermen could roflstomp all the others at the same time.