|I would say two, no doubt. Even though I loved 3, it felt rushed.|
Yea.. Season one is my favourite. There was character development, and they didn't rely on shiny* new Transformers to sell the show. They wanted to make all the good guys blind and wander through a forest, that's what they did. And other stuff.
*In the sense that the new Transformers were shiny. Animals, but shiny. In the bad way.
Too much marketing in season 2 and 3. There was a bit in season one (initial characters, add-on Blackarachnia, Tigertron, Airazor), but it wasn't every other episode.
Also, season one is the only season of any Transformers series (to my knowledge) to feature every single character having as a non-shiny Transformation Modes. Yep; all animal here.
Mine our 1 and 2. 1 because of the development. 2 because it furthered the story at a good pace. 3 to me was either a bunch of upgrades, new characters and deaths. And if it wasn't that some characters were just absent for like half the season.