There is not much to separate five-time Ballon d'Or winners Messi and Ronaldo, who are regarded as two of the greatest players of all time.
Both are all-time leading goalscorers for Barca and Madrid respectively, having guided their teams to Spanish and European honours.
"They are two completely different players," veteran goalkeeper Buffon told reporters on Thursday.
"Messi is more complete, because he starts deeper, has more technical quality and a vision of the game that is worthy more of a trequartista than a finisher.
"Cristiano Ronaldo, perhaps because he is a little older, has become a killer in the penalty area. Compared to how he was before, Ronaldo preserves his energy more, so he no longer goes out to the flank for a nutmeg or trick-shot, but with one ball into the box he can create a goal."
Messi tops the La Liga goalscoring charts with 25 for leaders Barca this season, three ahead of Ronaldo.
The Madrid star leads all scorers in the Champions League, however, with 12 goals to his name.