let me say this; both Leo and Cristiano are the two best players of our generation.

1. Lionel Messi is more versatile and dynamic. He has played as a right winger, as a CAM, as a False 9 and often drops very deep at the position of a CM for Barcelona and Argentina of late. He has been very successful in all of the aforementioned positions, vis a vis, controlling the game, creating chances, dribbling past several players with ease and scoring for fun.
Cristiano on the other hand is a little one dimensional of late. Over the last two years, he has concentrated more on scoring goals, and is not seen involved in build up play as much as one would like him to. He preys on the supplies of his team mates. He is a prolific goalscorer.

2. Team player- Ronaldo and Messi are both the talisman for their respective teams . However, as a United supporter and follower of Ronaldo since 2003, I have noticed that Ronaldo is a tad bit selfish. Most strikers are selfish. But his recent expressions of exasperation at Bale and Arbeloa for not letting him score have pretty evidently reflected how he values personal goals over his team. Messi on the other hand is a perfect team player. Even when on the verge of a hattrick, recently against Cordoba, he let Neymar take the penalty. It was a great show of sportsmanship spirit and the kind of bonding and understanding he shares with his team mates. He values teams performance over personal achievements.

3. Success with National Team- Leo Messi is a clear winner in this aspect. He won an Olympic Gold with Argentina, has taken his team to the final of last years World Cup, even when all the Argentine strikers put up a horror show and misfired left right and centre.
Ronaldo hasn't been poor with Portugal, but his performances have not been exceptional either.

4. Play acting- One huge quality Messi possesses is that he never goes down easily on the field when tackled. He never play acts. I have hardly ever seen him diving.
Ronaldo on the other hand has a terrible reputation of diving. He has been booked several time for simulation and often times he gets away with dives to earn penalties. He used to do this at United as well.

Statistics- Messi has 452 goals for club and country in 575 appearances. Ronaldo has 481 in 739.
Quite clearly, Messi is ahead, statistically.

Aside from all these points most pundits, former players and coaches, who understand the game better keep Messi ahead of Ronaldo.
Also, from this generation, Messi time and again has been hailed as the all time greatest(which is very debatable).

Ronaldo at United was dynamic winger who could score and get past players at will. However at Real, with his quest for Ballon D'or he has become more of a great goalscorer. Nothing more, nothing less.

Messi, indeed is the better player and the greatest of this generation.

You people have started again. You are not tired? Enjoy the two players while they last, because some day they will hang their boots. Only when they have stopped amassing any record you can now sit down and judge better who is the greatest in this generation. until then, Ronaldo is Ronaldo and Messi is Messi.