most likely sony... nintendo would wait till they find a truly compelling reason to use head tracking, which would be forever. sony tend to push these kind of technology faster out the door.
so i would be really surprised if nintendo does this first. they do have a greater commercial stake in making a game like this though, more so than sony, since the wiimote is a pack-in and everybody has it.
and please, it has nothing to do with graphics.
the Wii is an epidemic.