My favorites were Bluestreak (cool colour scheme), the Powermaster Optimus Prime, the two Headmaster Monstercons and Cloudburst, one of the Autobot Pretenders. The only Transformer that I relentlessly bullied my parents to buy was Jetfire. It might have been based on a much older animé robot, but I still loved it.
However, I do think that the later rip-off releases (especially the Actionmasters) devalued the range. They were running out of ideas and it was pretty obvious that they were desperate to keep finding new 'novelty' ways to sell toys. With that in mind, I think that the Rodimus Prime toy was the very worst ever produced.
Oh, does anyone else here think that the 1980s/90s comic series was far better than the Saturday morning cartoon? I thought that Marvel comics created an excellent set of characters, a coherent back-story and exciting story situations. What a pity that they had to ruin it by forcing the story writers to copy the characterisations and story of the cartoon. Grimlock went from a brilliant, charismatic commander and a brave warrior to a mis-wired moron and who talked like this: "Me Grimlock munch on 'Con!"

A traversty!