What? No Movie Birthday Cake Optimus Prime?
lol
Anyways, as THE one as the G1 prime, I'm going to have to exclude WfC and FoC Optimus Prime, as they are in their own awesome reality separate from G1.
Same with WWI Optimus Prime, another branch in the multiverse.
Hmm......... I'm going to have to go with Hasbro's MP-10 when it comes out.
As for what's in my collection, Classics Voyager Optimus Prime as the current incarnation of THE Optimus Prime.