>>1205764There aren't that many, so you could just look through a list of them:
https://myanimelist.net/anime.php?cat=0&q=&type=0&score=0&status=0&p=0&r=0&sm=0&sd=0&sy=0&em=0&ed=0&ey=0&c[0]=d&genre[0]=18&o=2&w=1&o=2&w=2
The ones that are still popular to this day are likely the ones most people would consider "the best". Astro Boy, Gigantor, Cyborg 009, Mazinger Z, Getter Robo, and Time Bokan being some titles among that list. I'm not a huge mecha buff, so there might be others in there that are considered important, too. Some of them might be riding off the coattails of the manga's success, though.
Also, honorable mention to Ideon, even though it came out a year later.
