One set of categories I was thinking of, to try to cover as much as possible of the Brand would be eras...
- 1980s (mostly Gen1)
- 1990s (mostly Beast era)
- 2000s (mostly Unicron Trilogy and Animated)
- 2010s (mostly TFPrime/RID and Prime Wars)
- New Movies (Movie Universe, because next year it will have been around for a 3rd of the time Transformers has existed)
- General Knowledge (for questions that span multiple eras or don't relate to a specific era).

The other set is almost the same as Trev's, with Toys, comics, cartoons (which covers the 1986 movie) Live movies, and General Knowledge (for questions that don't fit into the other categories). The sixth category could then be "behind the scenes" dealing with the people and businesses who have created elements of the Brand over the 30+ years.

But let's see what other ideas there are...