What people here are not taking into account is that, for an attacking player, dribbling and beating your man is the most dangerous thing that you can possibly do to a defence. When a player is beaten, the team shifts positions in order to cover for the man; this opens up a massive amount of room comparitively. This is particularly dangerous when you have a good passer on the ball to exploit the situation.
Messi, in terms of dribbling and close control over a football, is obviously unrivalled, and is a truly fantastic passer of the ball. He absolutely shits over Ronaldo in these aspects. His decision making is also years ahead of where it should be, which equates to one hell of a player. When Messi is on form, the opposition defence is literally all over the place due to the havoc that he can cause it. This doesn't just leave room for Messi to exploit....
It's all well and good saying that Ronaldo is better in the air, better finisher, two footed, etc, yet he is not as dangerous as Messi when it comes to opening up a defence. I don't believe it's as simple as "Messi is a better dribbler and passer, but Ronaldo's better at heading, finishing, etc", and I wouldn't think it'd be outrageous to suggest that there is some sort of hierarchy in regards to these attacking attributes. Dribbling is the single most damaging asset for an attacking player, in my opinion, and Messi is phenomenal at it. When was the last time we saw Ronaldo regularly take control of football matches and dominate them? 2006/07 is the answer, when he used to beat his man with the use of sheer power and agility. Ronaldo is a different animal now, albeit a fecking brilliant one in terms of productivity. However, I can't help watching him and yearning for those attributes that originally drew comparisons with Best.
Perhaps it really is just preference; Ronaldo is the complete forward, Messi is a magician. It depends on whether you want a player who can win a match, or a player who can dictate it. I'd take the latter every single time, and it's why I'd take an on-form Rooney over Ronaldo also.