But when you look at clay achievements my rank by most impressive. For me it would be Federer>Courier>Djokovic
But djokovic is only 24, He might win 4rg (not that I'm putting money on that!)
You, are right. Federer wins against Courier not only because subjectively I think he is greater on clay but he has actually achieved alot more than Courier on this surface. Djokovic only wins because I think he is alot better than Courier, but with objective reasoning you cant say he has achieved more than Courier on clay.
However, I was asking for subjective analysis of their greatness on clay and not counting numbers.