The most evil Megatron was the armada version(Dreamwave comics). He wanted to conquer the universe for the sake of ultimate power and greed. He treated is Deception like trash he treated them like object that were a mean to an end in order to achive his goal and he saw the minicons has a tool of power he did not look at them sentient being this behaviour is evidenced on the way he treated leader 1 his own personal minicon. The G1 version so himselve has the good guy.
G1 Megatron was ruthless and aggressive but hes was not pure evil like armada megatron. Armada Megatron wanted power for the sake of power he so his own troops has mearly tools achive his own goal. G1 Megatron was a fighting a course that he belived in he had a purpose he only drawbacks was that he method were higly aggressive, he was extremly vengeful and he also liked power but at heart he4 was still fighting for what he belived in. Megatron from the prime was fighting to end the caste system on cybertron it was established in the novel Exdous he and prime friends at one time.