I would be the apprentice of Axel - The Flurry of Dancing Flames
You are the "heart" of the Organization XIII, Axel and you constantly planning to end the boredom and silence within the Castle that Never Was. Together with you firends, Demyx and Roxas you'll mess up the life of the other members a little bit. Searching for someone to mess with Vexen's experiments or cut small figures out of Luxords cards? Your the one to do it! And although you get a lot into trouble, you're still skilled at fighting and controling your element, which's fire, by the way.
The only thing you lack is that you tend to understimate your opponents and therefore, if loosing to someone, loose pretty bad. The others either love or totally despise you, most of them not knowing wether you're really a friend or going to cut their throat the next moment. Since you don't get along with the Superior and his "pet", Saix, very well, you're most likely to leave the Organization one day and follow that non-existant heart of yours....
Members with whose apprentices you'll probably get along with well: Demyx, Roxas, Larxene
Who you should look out for: Xemnas, Saix, Xigbar
As long as I'm with Axel, I'm good.