I feel like I’m kind of cheating here because the answer is so easy, and the reason it’s so easy is because I’ve seen so few mecha anime series. My favorite is without a doubt Code Geass: Lelouch of the Rebellion, both seasons. It was either the fifth or sixth anime I ever watched all the way through. It’s in my top ten favorite anime because of the timeless story, deep characters, amazing music, and cute and impressive CLAMP/ Sunrise art-style.
To be honest, the fact that Code Geass is a mecha anime had nothing to do with why I watched it at first or why it quickly became my favorite. On the second watch, though, I started to enjoy the mecha side of things, although my understanding of what makes a good mecha anime was and still is very limited. I remember thinking the designs of the robots were awesome and I wished I could draw them. (I can make halfway decent sketches of animals, but objects and things with consistent, measured shapes and straight lines… I can’t draw those at all.) I loved that the mechs were all 2D without 3DCG.
Now that I’m thinking, I guess I have a few ideas of what should make up or be included in a “good” mecha anime. There should be a dramatic or entertaining story beyond just robots fights. Yet, the majority of action scenes should be robots fighting robots, or other enemies. How the mechas look (2d, 3d, etc.) doesn’t matter as much as making sure there’s “robo-lore” explored in the series. For instance, how do the mechas work? Are they linked to the nerves of the pilot? What determines pilot/robot compatibility? What kind of fuel or energy does the mech use? Those three items should at least lay the groundwork for a good mecha anime.
Code Geass meets the three criteria. There’s a fascinating story beyond all the mecha stuff: the tale of Lelouch’s rise to power through ingenuity and iron will. Not all, but a majority of the action sequences, are fights between Knightmares. There is an ample amount of robo-lore, and if some of it doesn’t come across in the animated series, you can read about on the fandom wikis. The technology that powers the mechas, the Sakuradite Cores, are made from the Sakuradite mineral unique to the Code Geass world. Suzaku’s agility and response time make him more compatible with Knightmares than most other characters. So, in addition to being a great show on its own, Code Geass is a decent mecha show, too.
The few other mecha anime series I’ve seen include Ghost in the Shell and S.A.C. (if those count), Neon Genesis Evangelion (the series), Bokurano, Escaflowne, Kannazuki no Miko, Aldnoah Zero, FLCL, Gurren Lagann, and Darling in the Franxx. If I had to choose one of those as my favorite mecha (rather than Code Geass), I would definitely pick Evangelion. It’s just such a classic. Well, this has been Anime Rants covering Day 11 of the 30 Day Anime Challenge. Ja ne!