which RB to pickup on waivers?

C. Ivory, J. Stewart, J. Starks, J. Best or T. Choice?

*must start 1 QB, 2 RBs, 2 WRs, 1 TE, 1 K + 1 DE
(only have 13 roster spots for 8 starters + 5 bench players)

(2) QB's are Big Ben, Matt Ryan
(3) RB's are M.Turner, L. McCoy + L.Blount
(5) WR's are Calvin Johnson, Jennings, Nicks, S.Rice + my top choice to drop out of the 5 WR's is Mike Williams (TB)
(1) TE is Gates + (1) K is Crosby + (1)DEF is Jets


thanks in advance