Whilst I appreciate the fiction as representations of the toys - and it will often persuade me to buy a toy based on character (Sky-Byte was a great example), for me the engineering of the toys is what maintains my fascination with TFs.

For that reason I find (for example) Beast Machines a lesser line - as good as the show might be from a sci-fi POV, the Maximals really don't do much transforming. Most of them morph into quasi-animals, and in many cases (Nightscream, for example) are really badly engineered, with the various robot elements fitting together poorly if at all in beast mode.

There are some TF fictions which I love - G1 cartoon, Masterforce, RiD, Beast Wars - but ultimately the shows alone can't carry a toyline for me.