Most Fav Gimmick:

Combiners: This wins it for me, I love the fact that can unite to become something more. The evolution of the modern versions such as the HFG and the poseability we get are awesome.

Minicons: To link them as a way to find or bring out a hidden weapon is a clever touch.

Least Fav Gimmick:

Bodiless Headmasters: This I find is really annoying! What's the point of a headmaster that doesn't have a body??