Beast Wars first, then Prime, then Beast Machines, then Animated. I also like the Unicron trilogy, but not as much as the ones I said. All of the series I liked did it right: they took the established continuities and set it aside for the sake of the story they wanted to tell while keeping the core intact. They took elements of the series and rearranged them into something that works for that particular version of the series. More importantly, they limited the character set to about 20-25 characters, with about 10-15 core characters in total. That way we get to see some character growth with everyone.
I'm not a fan of the G1 Transformers. The story lines were bad, characters were introduced just to sell a new toy then forgotten about, and there was no character development. The characters were complete pussies as well. For being a supposed badass leader, that version of Megatron never really got into battle that often. He would also retreat from battle when one of his soldiers got hurt, something that a thug like him should never do. Sorry, but a leader like Megatron should never lead from the rear. He is good at battle, not strategy. He should be right in the thick of it when the situation calls for it.
Also, it was cobbled together from three different toylines, one called Micromen, another called Diaclone and from one of the Macross series. Ever wondered why Optimus and Megatron never shared screen time? Ever wondered why the Transformers turned mostly into cars and the Decepticons turned into walkmans, pistols and planes? Read this article and find out.
http://www.cracked.com/article_19470_6-classic-kids-shows-slapped-together-from-recycled-material.html
And no, I did not cry when I saw Optimus die in the 88 Animated movie. Around that time, my grandmother died and the death of a figment paled to the real one my 9 year old self had to deal with.
Everything I liked about Megatron was not in the G1 Transformers cartoon. Sorry, but it wasn't. All of you saw a better version of the character from other sources and your memory of that better version was transposed on the G1 Megatron. The core of the Megatron character you love was created by Marvel Comics, mostly the United Kingdom iteration of the comic book.