For me it's Kamme rider Buffa, at the beginning he really caught my attention the whole human or player can be greedy as hell. I feel like he's more a relatable character than other main cast and captures the reality of how cruel people can be to get what they want.
Juggler and Genm both debuted the same year, both characters become iconic anti-heroes of their respective eras. They even returned in a Reiwa entry. Juggler plays a role similar to Dan Moroboshi back in Ultraman Leo as mentor and captain when he returned in Ultraman Z, especially that with the reveal twist in the early episodes.
Kuroto meanwhile, returned in his titular spinoff, and eventually as one of the main characters of Kamen Rider Outsiders.