[MonkeyBusiness]

In terms of likeness to likeness, I'd agree that Ultra Magnus from the Transformers Animated line is probably closest. I'd say Masterpiece Optimus Prime is a close second though.

However, in terms of the level of difficulty from the original source material to the toy, I'd say Revenge of the Fallen's Optimus Prime would be right in there. I'm not sure there's been a more complicated character committed to plastic before, and with a little bit of paint RotF Leader Prime is pretty close to the big screen version.