You have used GNOME and KDE, but have you ever tried Enlightenment? If not, give it a try and I am sure you won’t regret. Enlightenment, also known simply as E, is a lightweight desktop manager for Linux which can be used alone or in conjunction with GNOME/KDE.
While most lightweight desktop managers shave out all the graphical effect and provide only a simple shell that perform necessary functions, Enlightenment works hard to distinguish itself from the rest. Not only is it simple, fast and flexible, it is also elegant, beautiful and revolutionary.