Hard courts- toss up, slight edge to Djokovic
Clay- Djokovic hands down
Grass- Djokovic most likely
Carpet/Indoors- Hard to tell when there are hardly any of these events these days and havent reached that part of season yet. Probably Djokovic again.
Djokovic has a ways to go to reach Agassi's place in history. However Djokovic of 2011 is having a better year by far and is a better player than Agassi was any year of his career, be it 1995, 1999, or any other. I dont see how anyone can suggest otherwise, and I am a bigger Agassi fan than Djokovic fan. 2011 version of Djokovic matches peak Agassi in ball striking, matches him in returning, is light years faster and better defensively, serves much bigger, volleys better, and is tougher mentally.