I don't think mcgahee gets enough credit for his short yardage ability. He's still just as good as a Steven Jackson in that aspect, and has about the same amount of wear and tear. He's a good pass protecter too. It's catching the ball and fumbling that were the big issues with him last year, but I think he could still give a good year or two as a short yardage back.
Moreno is average at best as a RB...good receiver out of the backfield though.
Hillman was marginal last year but brings some speed and should get better this year.
I'd rather cut Moreno and pair a rookie like Lacy, Bell, or Michael with McGahee. Willis in a number two role will be better than Willis in a number one role, like he's had to play the last few years.