Art Tek, Zenith forge [Painted black], Workshop, Hasbro [flat gray primer] Before After This is by far the most detailed head, but also the smallest it looks a little small when paired with the Iron factory kit which adds bulk, the head is about the size of his fist. However it is easy to put on and take off. Shame it doesn't come in black though, as that'd save me the issue of painting it, but no big deal. The light piping doesn't seem to come out, which is a shame as I really wanted to pull it out and paint the rest of the head in black. Might do that, but it will be a lot more difficult to paint it all without being able to remove the head. So, evaluating each head: Hasbro/takara Fits with screws, looks nothing like g1 grimlock. Light piping. Medium size. Detailed. Arttek Solid 1 piece. Light piping. Pops on with a ball joint. Large. Detailed. ZF 2 piece. No light piping. Screws together. Have to work to get the head to hold together. Screwholes prone to breaking. Medium Large. Less detailed. Workshop 1 piece. Lightpiping. Pops on with ball joint. Smallest. Detailed.