Great topic SharkyMcShark
I really loved micromaster combiners as a kid, sheer giddy joy in creating a space shuttle tow truck
I also really liked the turbomaster/predator missle launchers. They really packed a punch and I used them to shoot down all sorts of things.
I never owned one but the G2 Aquaspeeders water pistols looked like fun
Finally just combiners in general were probably the most iconic and mindblowing of all transformers gimmickry.