7. MechaGodzilla (Heisei) - Of the three MechaGodzillas, 'Super MechaGodzilla' is my least favourite. While his arsenal of weapons is pretty cool, he is let down by a pretty bad design. His head looks a bit goofy considering he is meant to be made in the image of the not-goofy Heisei Godzilla. He also looks far too shiny and comes across as more plastic than metal. If he had a better, more appealing design. He would probably be higher on this list.
6. M.O.G.U.E.R.A. - In my opinion, M.O.G.U.E.R.A. is a pretty bland 'robot'. While I prefer the original to the version seen in Godzilla vs. SpaceGodzilla, I'm including this version on the list as it was the only design to appear in a Godzilla movie. I'm not completely sure what to say about this character other than the fact that it's weaponry is decent and is only higher on this list for having a design not as bad as Super MechaGodzilla's design. The yellow plasma shots that come from it's eyes are pretty weak and pathetic though.
5. Mechani-Kong - Now we are finally getting in the characters on this list that I like. While Mechani-Kong isn't impressive in terms of weaponry, he has a simple but like-able design, and the fact that he has what are essentially grenades strapped to him is pretty awesome. I also like the inclusion of the blinking light on his head that can subdue living, breathing monsters like King Kong himself. It's also pretty neat knowing that he was considering as one of the villains Godzilla could fight in the Heisei series. However, he's only at Number 5 because of the fact that the supposedly inferior King Kong was shown to be more useful in the film, seeing how the villains go out of the way to capture him to perform jobs Mechani-Kong could not do.
4. Jet Jaguar - The first Mechanical Kaiju to appear in a Godzilla film (unless you count Gigan, which I don't), Jet Jaguar isn't exactly the most amazing character to make an appearance in a Godzilla film. However, I think that his bright colours and 'wacky nature' is part of Jet Jaguar's charm. Plus, he has his own theme song. I really like his ability to change size and I find it brilliant that Godzilla went from some tragic warning of atomic weapons to a cute-looking 'dinosaur' that teams up with size-changing robots to fight an insect with drills for arms and a gigantic cyborg chicken.
3. MechaGodzilla (Showa) - This incarnation of MechaGodzilla was the first of the current three (unless you count the rebuilt version of Showa MechaGodzilla) and is my second favourite of them. He has the perfect 1970s Showa look and looks far more menacing than the version that would later show up in the Heisei series. He has a very impressive arsenal of weapons and the inclusion of a Force Field brings him up to third place. He's also one of the few monsters to have ever made Godzilla physically bleed. I've also got to say that I really like the suit used for his Fake Godzilla disguise. I'd love to have seen Godzilla look like that in one of the Showa films.
2. Kiryu - Despite being oddly named as Kiryu instead of MechaGodzilla, this is my favourite incarnation of the robotic Godzilla double. What intrigues me the most about this MechaGodzilla is the story behind it. While the first MechaGodzilla was simply controlled by aliens and the second by humans, this MechaGodzilla is made from the bones of the Godzilla from 1954, keeping it's memories from it's past life. It also allows this MechaGodzilla to have better movement, including tail movement. The fact that it can actually communicate (via the computer screen inside of it) is also unique and the fact that it doesn't exactly want to fight is a bit tragic. His arsenal of weapons is also pretty awesome. I especially like the missiles he can fire, and the 'ice beam' in his chest.
1. Mecha-King Ghidorah - This is my absolute favourite mechanical Kaiju, and it isn't difficult to see why. King Ghidorah is already awesome (and weird) enough as he is, but he is exceptionally awesome when turned into Mecha-King Ghidorah. I love the robotic neck and head that replaces the one Godzilla destroyed, and the metal body armour is also a nice touch. I love the capture cables that it can use to paralyze it's opponents and is a very tough villain for Godzilla to fight. I also like the idea that this creature is pretty much a dead corpse with metal parts inside of it reanimating it. That's pretty messed up and/or creative.