On clay ! It's not his best surface, of course, but I love watching him in Roland Garros, it's simply the greatest tournament for the french players, the matches often are dramatic in the 5th sets. Sentimentally it's different.
And Seb never could have asked for the empire to check to mark during his match against Nadal on another surface ! *provocation*
No seriously, I really don't like grass, I don't have many occasions to see Seb on this surface but, even if he plays well on, it's too fast, too schematic, too insipid for me. Moreover I don't like the general atmosphere, the crowd is unexistent, everybody in white is boring...no emotions.
I like to see him on hard courts like in Melbourne, Key Biscayne, Bercy etc...