My favorite OS is the command line environment. Of course someone, after using the CLI for some years, may reach the vision of the Unix gurus of yore. Text interface is king. You can read and understand the text a program outputs and change it. You can pipe that text unconstrained by the developer of the original program. In the GUI, for example, you cannot pipe something you wrote in notepad to windows media player.
Of course the command line environment falls short without Stallman free software because:
1) someone could change notepad to allow it to output on the command line
2) someone could change media player. add a flag --ascii-video-input '-' to read ascii video frames from standard input