Who would you pick? Its nearly impossible to say. The two best players on the planet, I think that's a given. But who is better? Some people will claim Messi, others will claim Ronaldo. In my opinion, Messi just shades it, only just.
I have heard a lot of criticism about Ronaldo, particularly about his tendency to dive or how his show boating sometimes aggravates other players into making malicious challenges. However, look at his current record for Real Madrid. 45 appearance, 43 goals? That is absolutely magnificent from a player who isn't specifically a forward.
The only thing Ronaldo's game is lacking, in my opinion, is his defensive contribution to his team. Rarely do you see him bust a gut to make a tackle. He is a class act though, you can't deny it. Heading, shooting, free kicks, control, skill, pace, strength, he has it all. His record from Manchester United proves this, particularly his tally of 42 goals in one season, helping United to Premier League and Champions League glory.
Again, I think Messi's only fault is his defensive game. Despite this, he is an absolutely majestic player, and I have never seen any left back get the better of him. His control when he runs with the ball is second to none. His scoring record speaks for itself, 105 goals in 158 games is quite a record for a player who spends most of his time in the wing.
So, in conclusion, it is my opinion that Messi comes out on top in the competition of who is the best player in the World, but only just. His consistency, ability to win any game single handed and the face he has achieved so much at only 22 years of age gives him the edge over Ronaldo. There will be a loot of different views on this topic, this is mine.