What do you find to be the most productive desktop environment?
My personal favourite is XMonad. The easy-to-use keyboard interface allows for a quick and responsive way to deal with programs, rivalling the power of the command-line, yet including the options of the GUI. Furthermore, the simple and straight-forward design runs and works faster than either GNOME or KDE, and the tiling system allows for an efficient task-handling device. In addition, it is written in Haskell, and is more stable than most other desktop managers.
Therefore, I believe that XMonad provides the more efficient and productive environment.