I think it is Allen the Alien in both the show and the comics. He is a good guy and willing to accept people as they change but still is flawed in his devotion to institutions which he sees as immutable. It is an interesting contrast and admittedly the flaw side doesn't come up too much.
I'll get started: can't exactly say why, but I freaking love Debbie. She might be my favorite "mom" type character in any show I've seen, honestly her interactions with Mark were what initially kept me interested in the show (especially the backyard scene).
Though she's of course not much of a character in the comics. It's much harder for me to pick a character there, but it'd have to be either Nolan, or
Comics spoilers
Dinosaurus. Such an interesting concept for a character, and such a tragic end to both him and his human side.