By lines, or things that kinda belong together. With the exception of CHUG, that's broken up into 1984-85 for Autobots, then 86 plus new IDW and other Autobots, then Decepticons, then seekers on separate shelf, so 4 shelves total. After that I have Combiners from all series on an Auto shelf then Dec shelf. The rest is by toyline.

Newer stuff replaces older stuff, so once I have the denesity a line gets its own shelf, it there are lots of characters then they get split into Auto/Dec, so at the moment I've got an Autobot AoE Shelf and Galv/Lockdown are in storage. They might come off soon for Robots in Disguise stuff ... Need a more display shelves ... I've now got two massive tubs full of transformers and I'll need to get a third soon ...