Manchester United have boasted some of the game's greatest ever players but who makes it into their all-time best XI? The competition is fierce as Old Trafford has played host to so many legendary talents, from the Busby Babes in 1950s to the 1968 European Cup winners and the Treble winners of 1999. Who plays in the heart of the defence, Jaap Stam, Steve Bruce, Nemanja Vidic or Rio Ferdinand? And how can you ever possibly separate Paul Scholes, Bryan Robson and Roy Keane? It gets even harder when having to choose between Ryan Giggs, David Beckham, Cristiano Ronaldo and George Best. Up front...