Depends what you mean. Ronaldo is currently the best either have been at any point in their careers. Over a longer period messi maybe edges it on stats due to assists.
After seeing the "showdown" at Old Trafford a month ago I was really impressed with the way everything Argentina did went through Messi. He just doesn't lose the ball when he gets it and uses it so well. There is less show in the way he works than Ronaldo and is so clinical.
When he was substituted Argentina's game lost any kind of fluency.