I'd have to say Saix or Xaldin, more then likely Saix, he seemed more aware of everything, but I say if we got to know Xaldin, or Xigbar it could be one of those two, after all Xigbar did fight Keybladers before or just met them before. Xaldin was just hard, and also seemed really skilled. Here's a list of my belief with negative comments.
Xigbar because of how he fought Keybladers before, however his attitude is what he lacks in.
Xaldin due to his skills, however his want to stay and fight instead of evacuating to fight another day would also lack him in superiority since he would probably fight Sora the first time they meet.
Marluxia is a definate no, however he did have goals to become one, his power hunger is what he lacks in.
Saix due to him being the second in command, I see nothing wrong with him to be honest.
Luxord - Maybe, he seems rather wise, however the card things is the only thing I see him lacking in, as well as once again personality
Demyx - Straight up no,unless you want the Order to just fall down and collapse.
Axel - Maybe, although he lets personal feelings get in the way.
Larxene - No
Zexion - Possibly although he is still an enigma to me.
Lexaeus - Hes fine as he is, dead.
Roxas - This would be nice, the superior being a Keyblader like Sora I would have to go with Roxas in some ways for suspense issues.
Vexen: Blegh experiments is his downfall
Xemnas (Even if it's all besides him) Although he is already the superior, if any of the others were superiors, I still would go for him. He seems to have respect from most of his Order members and feared by most as well. He seems calm and knows exactly what he's doing, and mostly always seems to Control the Power, and not let the power control him. Something that should keep the Organization respected.