[Altaru]

My votes up for...

(you probably guessed it already, lol!)

Kenpachi Zaraki!

For one thing, only the most powerful people can even CUT him, let alone beat him. For another, he's able to hold his own against TWO (probably even more) court guard squad captains on his own.

Not to mention, he LITTERALLY fights alone. He has no help whatsoever, even from his sword, most of the time, and when he does have help he just has the helper choose a target and leave the area.

Let's not forget... He has an EXTREME amount of power on his own. His sword is still technically in it's sealed/Shikai form (depending on which you believe. I like to think it's still sealed, meaning Kenny has two more levels of power to explore), so he hasn't unleashed even HALF his full capacity of power.

Thus, I'd have to say that if Kenpachi were ever able to simply communicate with his Zanpaku-to, let alone unleash his Bankai, he could easily hold his own even against perfected Hitsugaya (who could apparently even beat General Genryusai Yamamoto).

Incidentally, I'm still waiting to see how powerful little Yachiru is as well. If she grows up to be anything like her father-figure, those two would make a completely and utterly unstoppable duo.


Runner-ups:

Aizen: I hate the bastard, but the whole thing his Zanpaku-to can do with illusions is ingenious, and just plain not fair.

Ryuk (DN): All he needs is a pen. Seriously. He can see your name just by looking at you, he can't be killed by any human means, and for that matter, the only way he can die is if he purposely saves a human, which he won't, lol.

There are others, but I'm drawing a blank on names right now, lol.