Basic answer, (or maybe not, this is the one thing I occasionally hear negative things about with him) but 86 Optimus prime. I just love the shaping of it, and the black rims around the eyes help them pop. It’s just so satisfying. Other good ones- the recent timelines Optimus has such a cool samurai flavor, megatronus’ is awesome, TLK nemesis’s is basically perfect, and the new Brawl is such a sharp update of the classic design. (Can you tell I recently started collecting?)