At this point, I'm not considering Bernard Scott a part of the conversation.
He's still dealing with injuries, so it's hard to say if he'll even bring anything to training camp.
Regardless, both Cedric Peerman and Rex Burkhead will be fighting for a spot on the roster in training camp. I think it'd be good for the team to have both players, but I do not know if the Bengals can afford a spot for a fourth running back.
Peerman is a veteran who showed a lot of power and decent speed in limited playing time last season. He was finally given legitimate time to show something and he did. It will be hard to leave out a player like Peerman, who proved he at least needs another look.
Burkhead, meanwhile, was the Bengals' sixth-round pick in April and there's a lot of potential there. He's a smart runner who runs hard and had an outstanding career at Nebraska where he averaged 6.8 yards per carry as a senior.
Either of these men will add a good third-down option to what should be an already-stacked running back corps with BenJarvus Green-Ellis and Giovani Bernard. A third dimension will be key for the Bengals in order to throw opposing defenses for a loop.