Which character would you consider to be the most solid, steady? and why?

I would consider Linda Loman. She is the dutiful, obedient wife to Willy and mother of Biff and Happy, Linda Loman is the one person who supports Willy Loman, despite his often reprehensible treatment of her. She is the moral center of the play, occasionally stern and not afraid to confront her sons about their poor treatment of their father.