Who cares? Volleying is a dead skill. It's like asking who is the best at swordfighting, or who is the best at speaking Latin.
Seriously, though - volleying played an important part in this year's Wimbledon final, with the eventual champion winning over fifty points at net. So rumours of its demise have been exaggerated somewhat.
And Nadal is a better volleyer than Djokovic, clearly, although he applies it less these days than he did back in 2007/8.