The reason Tony picked Gigi as captain was because he hated Ralph. The Aprile crew didn't like Gigi because he was an outsider from another crew. However, Tony couldn't change his decision because it would make him look undeceive. When Gigi dies unexpectedly he makes Ralph captain. Remember that scene? Ralph was so relieved and he told Tony to have a drink with him. Tony just got up and left without saying a word. Tony basically said "I promoted you because you deserve it, but I still don't like you." Great scene.