They’re staring each other down like Ali and Frazier on the cover of Rolling Stone. Kanye West vs. 50 Cent in the heavyweight hip-hop battle for the ages, which begins Tuesday (Sept. 11) with the simultaneous release of the stars’ latest CDs. 50 is vowing to retire if West outsells him during their debut week. Kayne, who has the better album according to the consensus of the critics, is playing down the rivalry admitting that the whole thing is a brilliant PR campaign designed to help both artists. Who will be the king of hip-hop? The better question: is hip-hop dead?