In Aligned, they came up with the idea that Optimus and Megatron were friends pre-war but eventually, they fell out hard and are now bitter enemies. The live action movies (at least in the original idea) had the idea that they were brothers. "We will always be brothers. We are bound together. You cannot escape me, brother. I will hound you across the stars if I must, until every star in the galaxy has burned itself into a cinder. I will hunt you, and I will find you, and when I find you, [clenches his fist] I will, as I promised, see what the Core might have sequestered inside the body of the so-called Prime." "Hunt me then, brother—if your hunt means Cybertron will escape your madness." Whereas in Animated, Megatron has barely any idea who Optimus is... and it isn't the final episode that he remembers Optimus's name. In Generation 1, this is their first meeting. "You've caused enough destruction for one day, Megatron!" "I've barely even started!" *Megatron's blasts harmlessly bounce off Optimus* "You...?! Who are you?!" "Your worst nightmare!" But what's you preferred take on their rivalry?