Definitely the answer to this is very complicated as both of these players are considered best football players in the world and no one can replace them as both of them are considered GOAT ( Greatest Of All Time ) players.
Ronaldo has more trophies as compared to Messi. Ronaldo can play with his both legs. Ronaldo can score with his wrong foot also. Ronaldo at 36 returned to Manchester united to his ex team. Ronaldo can take shot from long distance also. The shots taken are very accurate and convert that shot into goal. Ronaldo is better at taking penalties. His conversions in Penalties are very accurate. His header is also freaking good and he is considered God of football. As he scores in football ground the whole stadium goes cheering as people love him. So if you are a Ronaldo fan than cheers to that.
Messi is good at playing the game. He makes the game. Messi might not be as good as Ronaldo for taking penalties but Messi can do things that Ronaldo can't. Messi can't take shots with wrong foot and score a goal with wrong foot. Messi might be also considered overrated as people follow this guy blindly for the action he does.
Messi is also a player who can change a game within minutes with the agility to move fast in ground and using his brain. The tricks he does in ground while playing is unplayable and can lead to loosing of the other team.
In conclusion Ronaldo is much better player than Messi because he can change the game within seconds plus he can take shot with wrong foot also.