Personally, Ronaldo. His pace, strength, and ball control are mesmerizing, especially back when he was playing for Manchester United. He is a consistent big game player, holding a lot of Champions League and club records, and it pretty successful with Portugal as well. Messi has had a lot less success with Argentina (presumably because he isn't playing with a team of world-class players there). I'm biased because I support United, and never watched much La Liga, but also know that Messi is an amazing player, and it's hard to compare the two when they play in different positions and for different teams.