It's a tough question actually.

I love cybertron as it is what I rode back into the fandom on. I also like animated (the cartoon only), but I also like classics, because of their homages.

But overall it has to be G1. It started it all, and no matter what way you look at it, it is the series that is borrowed from in every single thing transformers related ever since. It is the single thing that has defined the very essence of transformers, and is the single thing that everything transformers is based off.