A Raisin in the Sun'scharacters of Asagai and Murchison are, as the previous posts noted, very different. The way they differ from each other makes them a kind of character that we call a "foil." A foil is a character that illuminates the important traits of another character by contrasting with them.
Asagai appears to the ideal black man in terms of his ability to deal with being black in America. Ironically, he is not American, and...
that is probably what gives him his unique perspective. He still has a close connection with Africa and the identity it gives him.
Murchison, however, is trying to function as a black man in a white man's world. It leads him to feel scorn for others, such as Walter, who are struggling to establish their identity on their own terms, instead of trying to mirror white society.
Asagai is portrayed in a much more positive light. We see him as strong, independent, and wise. The female characters are drawn to him. Murchison is whiny and shallow. None of the family particularly care for him, even Beneatha, who is dating him.
Hansberry uses the characters to examine two extremes in the black experience in America. It's obvious which one she values the most. The Youngers fall somewhere in between the two. By the end of the play, they have insisted on establishing their own identity on their own terms, even if it leads to trouble. They have moved in Asagai's direction.