This isn't so much as a question as to who do you think it would be as much as it is a question of how do you think he will pick his vp? One thought I haven't seen is the idea of him making it a democratic vote. He could do something like IRV where it narrows down all the choices and his VP is selected that way.
I thought of that because I just for some reason can't imagine Dean doing something obvious like picking Graham or Clark.