LooseCannon makes some very good points about the best way to handle end-of-game situations, but if we are simply talking about who is the best option to isolate and score - that guy would be Jeff Green. He has the ability to hit the outside shot, can get to the basket, can hit his free throws if he gets fouled, and has some relative experience in these situations.
Obviously he is not Kobe, PP, Melo, etc, but if we are not using Rondo to create the best opportunity, Green seems to be the best option.