I would agree with JBastow. Not only did he wreck defenses in England, but he went to Spain and became even better. Ronaldo is great with both feet and headers, while Messi tends to favor his left and doesn't score headers as often as Ronaldo. Messi's movement and finishing is unbelievable, but he essentially owes Barca his entire career due to the help they offered him while he was young...so I doubt he will venture away from Barca.
When it comes to being a teammate and not a superhero, I would chose Messi any day...but Ronaldo is a well-rounded force to be reckon with. And that's coming from someone who hated Ronaldo when he joined Man Utd. I've just grown to see past his attitude over the years.