This combiner topic is practically a 'personal rivalries' discussion now. I cannot resist making a few comments of my own, with a focus on G1 toys and rivalries I'd have liked to see.

- As a kid, looking at the 1985 catalogue, it struck me that Decepticon Triple-Changers and Autobot Jumpstarters should be rivals. Similar sizes, two each side, and gimmicks both based on transformation. Of course, a year later Autobot Triple-Changes and Decepticon Battlechargers complicated matters.

- I would have loved to see Shockwave and Ultra Magnus square off against one another (and they might have in comics, but I'm not a reader of those). Both big toys, both loyal deputies, both generally calm and collected. It might have happened if cartoons had depicted events leading up to the movie.

- Once more considering size, it would have been cool to have Galvratron take on Powermaster Optimus Prime, maybe even have the mad Decepticon leader re-issued with a Nebulon gimmick of his own.