We can probably start by tossing Alexander out, since Cincy is pretty good against the pass, and they have a pass rush which, against that offensive line, means Rivers is probably going to have a bad day. Again.
Of your RBs, I'm going with Sproles and Leshoure. You can move the ball against Atlanta, and Sproles looks like his old 100+ yards on 14 touches self. The Indy defense is suspect (but improving), and Leshoure will get goal line carries plus his regular workload.
It's true that Jackson is playing well and had a nice day last time out vs. the Niners, but I can't imagine that'll happen twice. And I don't trust Bush against a solid run defence and with Daniel Thomas coming on of late.