1. Micromaster Spinner. He comes with a Grandus.
2. Armada Perceptor. The components are small, but they have alt modes that should be small, and would be very unlikely to get a normal sized toy. This was a fantastic way to handle Minicons. On top of that, obviously, there's the combined robot mode. For what it is, it's awesome. Words cannot express my disappointment when Armada ended without ever giving us another set like this. The combining weapons are not even close to how cool this set was.
3. Micromaster Hot Rod. He comes with Star Convoy, and is a glimpse of a very different direction Micromasters could have gone, and possibly a missed opportunity. Micromaster versions of established characters might have done better. We'll never know.
4. Minicon Ramjet. He comes with Tidal Wave, and the ability to stow away inside the aircraft carrier is neat. We needed more Minicon interactions like this, not tiny cars pegged onto a normal sized car for some reason.
5. Smallest Transformers Ravage. I have to give it a nod for being the true smallest Transformer ever made, and I'm quite confident saying it is the smallest that ever will be made.