Thinking back to my favourite characters at the time, I can only think of likely candidates for two decades, the 60s and 70s: after that, most of my favourite comics tended to be more independent narratives rather than centred around a recurring protagonist. Exceptions would be things like Love and Rockets, but even that was a sort of ensemble piece with an ever-shifting focus. But anyway:

60s: The Black Panther:

Born in late 1961, I was a very young reader in the 60s, and the Panther probably became a favourite at first because I liked the visual image, but more thoroughly because I liked his quiet, undemonstrative, but effective way of handling himself and how that perfectly fitted the look. Obviously I wouldn't have articulated it in those terms at the time, but I do have some recollection of how I felt. He was one of the Marvel characters who played a large part in the daydreams I remember indulging in at the time, in which all kinds of different pop-culture figures would be mixed up, from comics characters like the Panther, Crystal, the FF, etc, to the Beatles, to Star Trek, to I don't know what.

Other contenders: Doctor Strange, Dormammu, Daredevil, the FF, the Inhumans in general but especially Triton and Black Bolt, ...


70s: Doctor Strange:

Already a favourite character from the Gene Colan run in the 60s (and the Tom Palmer/Dan Adkins issue that preceded it), Steve Englehart's run made this character possibly my all-time favourite to this day. His version feels so definitive to me that I've lost interest in anything that deviates too far from it - which would include almost everything since, for one reason or another. In contrast, the versions that preceded Englehart's seem like the same character to me viewed from a different perspective, or written in a different manner.

Other contenders: Shang-Chi (really the entire MoKF cast), Kull, Warlock, Howard the Duck, Thena, the Reject, Karkas (really the whole Eternals concept - it wasn't really character based even though Kirby created some of Marvel's all-time greatest characters for it), Valkyrie (more as potential than realisation), Moondragon, Mantis, Moon Knight, ... the only DC characters would be Kirby's New Gods, especially Orion and Barda.