Ronaldo easily
Done it in english/spanish/italian leagues
Broke just about every record going aswell
This is the crux of it for me, but you also have to factor in the impact on the international arena. Messi has by most accounts disappointed for Argentina. Unlike Maradona who singlehandedly led them to the 1986 World Cup, Messi has not inspired success in the national side (runners up in 2014). Ronaldo has been a huge influence on Portugal and for such a small and relatively poor country he was key to leading them to be Euro champions. I know he went off in the final injured but you can't deny his influence on that country. To do it in the three toughest leagues leaves no doubt to his greatness.