I saw KDB playing for Wolfsburg in the Bundesliga a few years ago. He was stand out the best player on the pitch then too. Brings a warm glow to think that Chelsea let him go. All the City players work so hard for each other, plus there is a lot of intelligence on the pitch, led by Silva D.
I agree KBD is their best player but would he improve us the most is the festive question? It pointless him player killer passes in front of smith!
I was going to say Aguero but KDB's wiki page describes him as being able to play as a second striker so has to be him. A consummate footballer.