As odd as it might sound, I wonder if taking a leave of absence from school is hurting Nathan, as he doesn't have that distraction (for lack of a better word) that he's had for the last few seasons. With the entirety of the focus on training for Beijing, it might be putting more pressure on him, which could be hurting him, in a way, and taking him out of the routine he's been following for the last few years.
Anyway, I voted Nathan, Keegan and Jason, though who the heck knows? I feel like Roman might go out there with something to prove, and he could be an absolute wild card (I predict he'll either medal, or be near the bottom - no in-between).