G1 Season 3.
The '86 Movie was the hilight really. Megs finally got to be the bad-ass we wanted him to be.
After that it was downhill, I couldn't really maintain interest in the cartoon the toys no longer interested me either. I saw bits of Beast Wars and lamented what they had dome to poor Optimus and didn't bother watching it for about another 10 years.. the animation and rendering were awful to me even back then. Beast Machines went under the radar. Later I saw bits of RID and didn't care for it either.
The advent of the BINALTECH and Masterpiece lines called me back to what I liked about Transformers in the first place - interesting toys with interesting characters in a decent storyline. The DW/IDW storys are mostly good too.