Well, let's take a look here shall we?
1. Xemnas
The Superior, Xehanort's Nobody, the creator of Organization 13, leader of all Nobodies. He has two red laser beams that look a lot like lightsabers, and wields the power of energy. He's pretty much pwnage.
2. Xigbar
A senior member, a gunner, a wisecracker, and an insulter. He uses two guns that look like a mix of a sniper rifle, revolver, and machine gun, with a mix of SciFish mechanics. He also uses the power of Gravity. Even though he could easily snipe someone off, at a close distance he is doomed.
3. Xaldin
Also a senior member, a lancer, rock hard abs, seems to be a silent type but actually a heavy talker, and quite the ladies man (nah his sideburns chase all the women away). He uses six sharp spears that float around and automatically attack for him. He also uses the power of wind. He could take out a bunch of people, but would eventually die.
4. Vexen
A long haired hippie, a scientist, a manipulator, and a shield... thing. He uses a spikey shield to guard against all attacks and it has a very short range. He also uses the power of ice. Perhaps he would be well defended and could maybe take out one or two people, but would fall quickly.
5. Lexaeus
The silent type, a muscled man, with anger management problems, and loves the power of darkness. He uses a huge tomohawk to whack his enemies into submission, and uses the power of earth. He is far too slow to do much, but if he hit it just right, he could really hurt people.
6. Zexion
A schemer, emo man, and weakling. He has no weapon or element and doesn't like to fight. The end. He'd be the first one to die, until he used his emoness to somehow get away.
7. Sai'ix
A ringleader, a quiet type, a mad man, a schemer, a tempter, and a manipulator. He uses a huge broadsword to really kick ass. He also uses the power of the moon and beserkerness to own anyone. Unless someone figured out to whack him with his own weapon, they would pretty much be screwed.
8. Axel
Roxas lover, Reno VA, fury of dancing flames, and a traitor. He uses chakrams to get owned by his own nobodies, and uses the power of fire to make cool backgrounds. He would get destroyed easily, and that's the end of that.
9. Demyx
Melodious Nocturne, a child, a blondie, and a bad actor. He uses a musical instrument, the sitar, to kill everyone, and the power of water. He would get laughed at, but basically take out Axel, Vexen, Xigbar, Zexion and Luxord without moving an inch.
10. Luxord
A gambler, announcer, actor, schemer, and trickster. He uses dice and cards to kill people, and the power of gambling. His "little game" could distract some people, but not really do anything.
11. Marluxia
A hippie, flower powered, girly man. He uses a huge pink scythe to kill people, and uses the power of nature/flowers to mega murder people. His powers could take out some, but it is minimal.
12. Larxene
A blondie, nazi, hyper women, and the only female member. She uses claws and dart... thingies to kill people really fast, and uses the power of thunder/lightning. She is really fast and sneaky and could assasinate some people without thinking twice.
13. Roxas
Axel lover, BHK, "the keyblade's chosen one", and Sora's Nobody. He uses two keyblades, Oathkeeper and Oblivion, to "pwn" people, and supposedly uses the power of light, because of the keyblade. He is tough but easily taken care of.
I honestly think that Xemnas would win simply because he has the most power and has control over all nobodies.
