With his "calm,God-like eyes" and
ears that heard more than was said to him, and his slow speech had overtones not of thought, but of understanding beyond thought.
Slim truly stands above the other characters. In fact, he is considered the one heroic character of Steinbeck's novella as he reserves judgment upon anyone and is the equitable leader of the men. Even when Crooks's name is brought up in reference to how well he pitches horseshoes--an activity in which he is allowed to participate--Slim placidly remarks, "He's plenty good." Always reserving any personal judgments, Slim calmly listens to the other men speak. Even when Carlson suggests that Candy get rid of his old dog, Slim is reluctant to offer any opinion, but he is wise,
He seemed to shake himself free for speech. "Carl's right, Candy. That dog ain't no good to himself. I wisht somebody'd shoot me if I got old an' a cripple."
Slim understands the alienation of the men, agreeing with George that the men become mean when alone too much. And, after speaking with George at length, Slim realizes quickly that Lennie is childlike and innocent, albeit very strong. It is this understanding that brings Slim to reach out to George. assisting him in the hilly walk back to the camp after George has shot Lenny in an act of mercy, saying "You hadda George. I swear you hadda." Importantly, he is the only one who comforts George.
Lennie is an admirable character because of his innocence. He does not know the harm he invokes and his death at the end makes him even more sympathetic. He is a likeable character if you feel compassion for him. He also has a childlikeness about him that is appealing to readers. You could say that George is a likeable character, because he takes care of Lennie, but in the end I think Lennie is easier to like.