Throughout Transformers, the face of good and evil as symbolized by typical alternate mode has constantly changed. It all started with cars and trucks being the heroes with jets, handheld & military equipment being the villains. Then the ranks fill out, the good guys get jets and bad guys get cars. We also see more animals in the Insecticons and Dinobots. Something starts happening though, and Decepticons get Terrorcons and Predacons and Trypticon. I think the third year/season starts the departure from Earth or futuristic jets or even military equipment towards beasts. The Targetmasters bring back the car/jet dichotomy, but the Headmasters blow it up with vehicles vs animals. Once again the Decepticon base former has an animal form. The next combiner, Piranacon, consists of sea animals despite being a "Targetmaster". The Clones show the emerging dichotomy of machine vs beast, with Autobot clones being a jet and car and Decepticons a falcon and puma. Powermasters retain cars vs planes. But Double Dealer has a Decepticon and Autobot mode, the former being a bird and the latter a missile truck; machine vs beast. Autobot Pretenders save beasts like Catilla have humanoid/warrior shells while the Decepticons have animalistic and monstrous forms. The new Autobot and Decepticon tapes are a tank & jet and a bird & gorilla respectively, and the Decepticons get an animal/monster pretender team. Beast Wars generally has the good guys as mammals, fish and birds, and bad dudes as arthropods (insects, arachnids, crustaceans) and reptiles (pterosaurs, dinosaurs). Beast Wars II changes it up a bit starting out with beasty good guys and machine baddies. Neo more or less follows the original Beast Wars model. Beast Machines... well, the bad guys are mechanical lifeless drones and the good guys are technorganic beasts. RID returns a bit to what we saw by the later terms of G1, good guy autos and bad guy beasts. Armada and Energon IIRC followed the original premise of military vehicles vs cars and trucks, for the most part. Cybertron just... everyone is anything at some point. Animated too had Autobots as, well automobiles and civilian vehicles and Decepticons as mostly war machines. Prime too seems to be in this direction. What's the best yin/yang opposite, or rather your favorite? Cars vs jets, vehicles vs animals, animals vs vehicles, animals vs animals, et cetera?