Picking two from Herron, Morency and Blumpkin is going to be tough. Herron is easily the most consistent of the three, he's not flashy but he gets the job done. Mo is probably the best reciever, and best at blitz pickup which makes him a very good 3rd down back. And Blumpkin probaly has the most raw talent and potential out of the three, i could see him making the #4 slot just because of that. So i think its down to Herron/Morency for the #3.
If they can manage to keep Grant, Jackson, Herron, Morency and somehow hide Blumpkin on the PS, i think everyone wins. But i fear he may have shown too much this preaseason for that to happen. It will be interesting to see how the RB's fair in this last game.
Its a shame that there really isnt anyone on the roster you could say is a "goal-line" type back, they dont have a davenport type guy. Maybe Blumpkin could be someone they develope into that sort of role? He seems to really be able to fight for the yards.