Remember one thing. If you include Carlsen in the list, you MUST include Caruana. Per Carlsen's own admission post the WCC 2018, he said, in classical time controls, there is no difference between the 2 of them. In that regard I would say the top 3 are
1)Carlsen
2)Kasparov
3)Caruana
Another school of thought is the amount of time one shows dominance in the game. Vishwanathan Anand has been in the world top 20 for close to 30 years now. I doubt anybody can claim that sort of dominance in the post-engine era. Purely for that, I consider him one of the best of all time (for now).
1)Carlsen
2)Kasparov
3)Caruana
Another school of thought is the amount of time one shows dominance in the game. Vishwanathan Anand has been in the world top 20 for close to 30 years now. I doubt anybody can claim that sort of dominance in the post-engine era. Purely for that, I consider him one of the best of all time (for now).