I've only been watching since 2018 but my favorite early on:
Seo In Guk - An AMAZING actor, can act in any role and make it his own.
Repy 1997 - serious, loyal & quiet
High King of Savvy - outgoing, athletic, full of love and life
Hello Monster - aloof , smart ,remote, & sophisticated
Squad 38 - charming conman
Shopping King Louie - adorable, lovable, innocent, sweet boy
The Smile has left your Eyes - total opposite- mysterious, unemotional , remote, uncaring, sociopathic until he falls in love and attempts to become good for the love of his life.