If you need immediate help, picking up Jacobs is a no brainer, as he'll always get 10 touches a game with a chance for a TD.
But if you're willing to bank on potential, I really like Karim and McCluster. Karim had alot of touches week one, and will have a domination on the Jags back field if MJD misses anytime. That doesn't mean he'll instantly be a superstar (it's the Jags), but he should be a decent FLEX play.
As for McCluster, is there any doubt he'll get 1,000 total yards this season? He already has 93 yards rushing on only 12 attempts (in two games where his team was smoked, no less), and won't go for negative receiving yards like he did against Detroit.
Other than Bowe, he's by far KC's best weapon. As a FLEX play, he should be good for 70 total yards a week with the odd touchdown. Of all the players listed, he's the only one with the upside to become a fantasy stud this year, as unlikely as it may be. viewtopic.php?f=18&t=497702