For me it"s: 1. George Best, 2. Eric Cantona, 3. Roy Keane, 4. Ryan Giggs, 5. Paul Scholes.
Although I didn"t have the privilege to watch Georgie in action (apart from videoclips and old footage) I think he was one of a kind. Something like Messi today. King Eric and Keano were the reason why I start supporting United in the first place (as for 15 year old kid from Croatia who"s started to watch football seriously). If you asking me, these three legends are among the most controversial and charismatic players in the history of football. As for Giggs and Scholes, they are true United legends. Do I need to say anything more apart from that !