Who Will Be The Chargers Third-Down Back?

Darren Sproles will be likely wearing a new uniform next year and he will be leaving his responsibilities to some of his former teammates. Antoine Cason already looks like he has taken over the punt return duties and we definitely will have someone new returning kickoffs. Who will be the back that Norv Turner chooses to go in on third-downs?
Will it be Ryan Mathews or will it be Mike Tolbert? Or will they even give the rookie Jordan Todman a chance to be that back?
Should it be Ryan Mathews? He better have figured out how to pass protect! He also had his share of issues catching the football out of the backfield. If he can’t block for Philip, we will see number 17 on the ground more often than we want and we can’t have that!
What about Mike Tolbert? He may be the better option, he is not much of a pass catching threat, but at least he would be able to keep Philip standing straight up. He still finds ways to make big plays when he gets his hands on the football also.
The rook? No way would I trust a rookie in that capacity yet. He wasn’t a pass catching threat in college and we saw what our rookie did last year in pass protection. Maybe he could surprise, but he has to prove himself.
Who is it going to be? Who will be that Sproles, Terrell Fletcher, Ronnie Harmon type of back for us this coming year on 3rd down? Whoever it is, I will be happy that Norv will not be able torun it through the middle on fourth-and-short situations with the lightning bug.