I prefer to use a close-to-standard layout because I switch between Linux/Xorg and Mac OSX and I wanted to have equivalent Emacs bindings on both; right now I've got:
Linux:
CTRL
SHIFT SHIFT | FN
META (alt) | FN | SPACE | SUPER | COMPOSE (alt-gr)
I use SUPER for all my window-manager key bindings, so they don't interfere with any standard bindings for applications.
And on OSX, SUPER = CMD and COMPOSE/META = alt (I still don't understand why OSX doesn't support a compose key).