By Kieran King The best player Sir Alex Ferguson coached at Manchester United was Cristiano Ronaldo. Ferguson signed Ronaldo, who was 18 at the time, for around £12million in August 2003 after he impressed during a pre-season friendly for Sporting CP against United. The Portuguese superstar endured a mixed first season before settling into life at Old Trafford and going on to become one of the best players in the world. Ronaldo scored an outstanding 42 goals in 49 appearances during his penultimate season at United before securing a world record move to Real Madrid for £80m. During his six-yea…