I'm still kicking myself for not picking up Charles at the end of last year, when I knew he was going up against some terrible, terrible run defenses. Look at the teams he cracked 100 yards against:
Oakland (fourth-most rushing yards/game allowed last year)
Buffalo (third-most)
Cleveland (fifth-most)
Cincinnati (they were good against the run, but he barely got 100 yards on 24 carries, not an overpowering performance)
Denver (seventh-most, he got 259 yards against a team that was losing their fourth consecutive game after being 8-4 and headed for the playoffs; think they might have checked out early?)
I'd hold out for someone more proven, but you've got to improve your running backs. Addai's not that good, AND he just got a concussion.
Spiller's a rookie who was late to camp, which may not be that big a deal but he's also playing behind a terrible offensive line. His game, too, is such that he's likely going to touch the ball maybe twelve or thirteen times a game - Reggie Bush-like. Not a workhorse, not the guy they're going to give the ball two three times when they're inside the opponent's five-yard line (and Buffalo's apt to spend a lot more time inside their OWN five-yard line, anyway).
Portis.... meh. Old.