I also think Chris Petersen would be a solid choice for them.
Maybe it's just me, but I don't see why Grudens name is being thrown around so much on espn and message boards. He has never been a college Head Coach before and only reputable assistant jobs were for a 7-5 Tennessee team as a GA and a 6-5 Pitt team as an offensive assistant. He had good teams in Oakland, however the second half of his coaching career was fielding average teams at best..
I think USC goes with stability here and a recognizable successful college name. I think it'll be Petersen, with an outside shot at chip kelly or possibly del rio (goes against my logic above, but he has publicly stated he wanted to coach for them and he's alumni so who knows)