Rivalry? What rivalry?From their embrace on the cover to their kind words inside, the stars of "The Voice" make it clear in this week's issue of Rolling Stone that any alleged rivalry between them is pure fantasy.Aguilera laughed off rumors from last fall that there was a rift between her and her fellow coach/judges Blake Shelton, Adam Levine and Cee Lo Green; she admits that she can be tough, but only because she has to be.Read More... More on Christina Aguilera