User blog comment:HozzieHozzbourne/Strongest champion outside of the game/@comment-10768370-20130920080125

My guesses are:

Vladimir, The Crimson Reaper

Since he's a blood mage he should be able to kill nearly every being instantly, he could let Syndra and Lissandra and hell even Kha'Zix explode, he'll even get stronger by absorbing their blood just like he did to his mentor. Xerath could be  a problem though since it's  a being of pure magic and Vladimir is pretty useless against him.

Hecarim, The Shadow of War

In his lore it's described that he causes dread to all nearby enemies and since he appears to be made out of spirits or magic he can't be slain that easily. He is also skilled in combat with his staff and he can summon spirits from the Shadow Isles. He could be weaker against mages since he has to come close to them to harm them.

Zed, The Master of Shadows

It is described that he has mastered an ancient and forbidden art, said to be allpowerful. He is also trained as a ninja so he's skilled in close combat. He can always summon his shadow to aid him and he has a group of Shadow-Ninja's to aid him.

Pantheon, The Artisan of War

He's extremely skilled with his weapons, he is said to be the best warrior of Mount Targon which is quite a prestation as everyone on Mount Targon is armed and dangerous. For Physical Strength I think he could match Darius and Kha'Zix but he'd be pretty useless against mages since he doesn't know anything about magic.