I think Messi is more complete for me Messi has everything however fails to utilise all his talent alot of the time. Ronaldo is alot more effective, hence why I think he's the better player because he uses his qualities more while Messi can really struggle against certain teams.
Messi has a fantastic header on him, that goal in the Champions League final was a gem. Problem being he is not so tall as Ronaldo so rarely finds himself chance to head the ball, so I find it hard to compare.