#4 Lionel Messi has played only in the La Liga whereas Ronaldo has proven himself in Portugal, England, Spain and will do so in Italy
There are many supporters of Ronaldo who have argued that Ronaldo unlike Messi has played in one of the best leagues in the world, besides LaLiga and has proven in tough conditions that he is the best. Ronaldo won the Ballon d'Or with Manchester United before he even joined Real Madrid. Ronaldo will no doubt continue to score goals for Juventus and bring more trophies with his goal-scoring prowess.
But let us not understate the fact that Barcelona is already one of the biggest clubs in football still and there is no reason for Messi to leave Barcelona. Messi has been consistently performing at the top for Barcelona not only in LaLiga but also in the Champions League. Before Ernesto Valverde, he was the main man responsible for the goals during the Pep Guardiola era winning 3 Champions league titles and also under Luis Enrique as well winning the Champions League in 2014-15. This debate will no doubt continue in the coming years as well.