Ronaldo is often on the periphery of games but always amongst the goals, Messi meanwhile is always amongst the goals but also always fully involved in the game. (Mostly)
Here's a post from Redcafe, most of which I don't agree with but the part at the end sums it up nicely.
'I don't. Depends on the footballer and what he says. I am not a Messi fan, I am a fan of the game and Ronaldo was one of my idols growing up. I loved him more than Messi.. to the point where I have a united top from 08 and a real top with the 7 on it. He is also a United legend, the team I adore.
The style of play I prefer is Ronaldo.. I love players whopperform tricks and have variety to their game rather than
a one footed boring dribbler... but even despite all these preferences and possible bias on my part, I can hands down say it is not even a fair competition.
Messi is just a different class, he has a touch of artistry to his game which is unbeatable. He has a finesse that only the likes of Zidane have yet he combines that with great explosive ability. . Hence why he gets so many goals, kind of like Puskas in that sense..
Ideally I'd wish he had more tricks in his locker and he was more entertaining like a young Ronaldo, but he is a footballing god that cannot be denied. On form he is simply something else... he makes Ronaldo look functional.
When I was younger I never thought Ronaldo would be described in that way, he seemed graceful and full of daring and panache.. he looked very hard to stop when he ran with the ball, only Cole at his peak could keep him quiet.. he gave Maldini and co a great game. But peak Ronaldo hasn't blossomed into a beautiful footballer. . He's a killer which is fine but he is competing with a assassin who isn't just more deadly but kills teams with the sheer beauty of hia football, dictating the game as well as winning them'
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The best argument you can make is not to argue at all but instead to post this link
http://fivethirtyeight.com/features/lionel-messi-is-impossible/