Compare Asagi and George.

Both Joseph and George appear primarily as male objects of affection for Beneatha. While each of them have numerous distinct qualities, they are both young black men. During the course of the play, Beneatha distances herself from George and grows closer to Joseph.
George is African American and apparently well off. We do not learn his back story—in the sense of family history that led to his prosperity. His concerns are for class status, which he identifies with assimilation into dominant white society. Personally, he is overbearing and unpleasant in his interactions with Bennie, mocking her and criticizing her clothes and interest in Africa.
Joseph, who is from Nigeria, is a relatively new friend. As he knows Bennie from college, he seems to have a better grasp of her aspirations. He is heavily invested in teaching her about Africa and even more so in encouraging her interest in her heritage. The idea of her becoming a physician appeals to him, because he knows how great the need is. As the play ends, he proposes marriage and asks that she go to Africa with him.
Hansberry draws an unexpected contrast in that the American man has the more conventional gender expectations than the African man.

Joseph Asagai is portrayed as a genuine Nigerian student, who is extremely attracted to Beneatha and wishes to take her back to Africa with him. Joseph Asagai is a champion of Pan-Africanism and rails against assimilationists. He encourages Beneatha to get in touch with her African roots and even gives her authentic Nigerian attire. Despite Joseph Asagai's affinity for traditional African customs and culture, he is a forward-thinking man, who supports Beneatha's dreams and challenges her to overlook western civilization's perception of success. Joseph Asagai is also a charming, compassionate man, who is both wise and charismatic.
Despite both characters being attracted to Beneatha, George Murchison is Joseph Asagai's polar opposite. George is a wealthy pedant, who values material success and embraces western civilization. He is depicted as a rather callous man with a superiority complex, and he does not support Beneatha's future aspirations. Unlike Joseph Asagai, George has very little in common with Beneatha and is more concerned with his social status than appreciating his African ancestry.