I don't get how people can claim that one is better than the other after all they achieved in the last 10-15y. It's mindboggling.
I rate Ronaldo higher but in the end, it's more a matter of taste than anything else.
They both are the core reason why their teams achieved what they achieved, both broke a sh*t ton of records along the way and they are without any doubt 2 of the greatest players to ever play the game.
Depending on how you decide to measure (since it's not really a science) you can argue that Messi is a more natural footballer while Ronaldo is pretty much the apex athlete but if you a look at their careers, the end result it's pretty much the same (with a few exceptions).
In on end, you have Messi that is a threat anywhere in the attack since he is just as good creating goals as he is at scoring them but when he's having a bad game / being shut down his team is pretty much playing with 1 less player. He doesn't run, he doesn't try, and just accepts there's nothing he can do to change the outcome of the match.
On the other end, you have Ronaldo. Easily one of the best finishers this game ever seen, he always seems to know where the ball is going to drop inside the box, can shoot with the left foot from any range, can shoot with the right foot from any range, he's the best aerial player I ever saw and although his playmaker abilities are seriously underrated he is one level under Messi in that department.
The big difference for me is that Ronaldo having a bad game / being shut down still scores or still tries to win no matter what the odds are. That mentality alone alongside his talent for me is what makes me rate him higher.
I honestly don't care who is the "greatest", I love watching Messi play and I love watching Ronaldo but at the end of the day, Ronaldo is the player I would want in my team.
PS: For all stat lovers out there, to make a fair comparison between both you should use stats from the 9y that both played in the same league since Ronaldo for most of his Man Utd career was a pure winger (although stats don't really matter without context)