The question has become football's biggest debate over the last few years, with fans on both sides poring over stats, trophy wins, awards, and everything else they can find to prove their hero is No1. And EA Sports has often silently waded into the argument, with the number that should settle it all - each player's FIFA rating.
It's hard to believe, but there was a time when Ronaldo was rated 13 points higher than Messi. That was back in 2006, when Ronaldo had established himself at Manchester United while Messi was still an exciting youngster looking to break through at Barcelona.
Since then, their FIFA ratings have fluctuated, with Messi overtaking his rival at one point, only for Ronaldo to pull himself back. This year, it's the Real Madrid man who's on top, by just a point over Messi.
On Thursday, there was a new wrinkle, with the Ballon d'Or going to Ronaldo, equalling Messi's haul of five trophies. Let the debate continue. Meanwhile, have a look at how each player has fared on FIFA in the video above.
Zinedine Zidane was given the tough task of selecting his 5-a-side team from former teammates.
His choice for goalkeeper was slightly surprising. Zidane of course was teammates with Iker Casillas, and the former Real Madrid keeper is regarded as one of the best-ever at his position.
Frenchman Fabien Barthez, however, got the nod in Zidane's team and it's understandable. Barthez's heroics helped Zidane win the most important trophy of his career, of course, the 1998 World Cup, so you can't blame the legendary playmaker for picking his compatriot.
The rest of the team is harder to pick. Zidane played with some of the world's best, including Alessandro del Piero, Thierry Henry, Luis Figo, Raul, David Beckham...the list literally goes on.
Ultimately, it was two Brazilians who made the cut, as Zidane picked former Real Madrid teammates Roberto Carlos and Ronaldo, along with himself.
Real Madrid goalkeeper Keylor Navas is more used to saving shots inside the penalty area than having a pop himself, but the Costa Rican showed he is handy enough with the ball at his feet.
He took on team-mate Nacho in the second part of Copa90's five-shot challenge - and showed off his class at the club's Valdebebas training base.
The 30-year-old was joined by the Copa90 crew to test his skills.