aronian or carlsen

objectivelly who is the stronger player

List the objective measures then see who does best and you will have your answer.

openings

middle game

endgame

tactics

posistional

overall chess understanding

openings

middle game

endgame

tactics

posistional

overall chess understanding

Ah you see I was thinking more like:

Rating

Tournament performances

etc

I don't think you can split chess into its constituent parts and compare players like that, because your strength is in the sum of the parts.

The Fédération internationale des échecs publishes a ranking of how the top players perform in a mixture of these categories you mentioned against their peers. These performance tests are called "games".
Currently Carlsen has 2872 points and is leading over 2809 points of Aronian.