Federer vs Nadal, Woods vs Mickelson, Ali vs Frazier. All are examples of the few unparalleled rivalries that have captivated the world of sport.
However, it is the ongoing battle between the two powerhouses of the football world that now dominates this exclusive group.
Cristiano Ronaldo and Lionel Messi play in the same league, for the two biggest clubs in Spain that form the fiercest club rivalry in Europe.
Pundits, players, journalists and fans - everyone has an opinion on who is the greatest.
All the boring stuff - the facts and figures point to only one winner.
While playing in the same league, Messi has scored 228 goals in 211 games compared to Ronaldo's 189 goals in 187 games. That's a goal to game ratio of 1.08 for the Argentine - a clear step above Ronaldo's mere 1.01.
Messi also has 22 hat-tricks compared to Ronaldo's 20, scored 91 goals in 2012 to Ronaldo's 63 and has 14 assists this year to just seven from the Portuguese player.
Honours from within the game further back up the stats: four times now Messi has won the Ballon d'Or. Ronaldo? Four times a runner up to him.
The evidence seems to be damning: Messi leads the way in goals and assists (surely the bread and butter of a forward player) and is still three years younger than Ronaldo. However, remember this is not a debate about the best goalscorer. This is a debate about the best footballer.
Messi's dribbling ability is his main asset. Perfect balance combined with searing speed make him virtually unplayable. Yet with Ronaldo you can't quite put your finger on what exactly is his strength, and that’s the point - he's got it all.
A supreme athlete, technically gifted, exceptional in the air, stamina, speed and an astonishingly accurate shot with either foot.
Roberto Carlos makes the point that Ronaldo is everything to Real Madrid, yet Barcelona are so much more than Lionel Messi.
To sum the rivalry up is best described in the words of Sir Alex Ferguson.
Having encountered both on many occasions, he stated Ronaldo is the better athlete, better technically, better in the air and has the best shot of the two, but he'd still rather have Messi.
Perhaps this is the only conclusion that can be drawn. The stats don't lie; the most effective player of the two is undoubtedly Messi.
Yet the most fluid, rounded and complete overall football player we have ever seen is Ronaldo.
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