Not sure I can answer that question-everytime I think I would chose techinque "x" I think of a reason technique "y" would be better.

Also thinking I would spend the time on "techniques" that might not be punching and kicking and grappling--thinking more of awareness and avoidence training.

If it has to be a single actual "technique" then I an leaning toward thing that would be illegal outside of "I did it to save my life" kinda things--something you would ONLY use when there was no other choice but to cripple/seriously injure someone.
I did battle with ignorance today.......and ignorance won. Huey.