If you could pick one technique...

[marie curie]

for kaju- probably snapkick to the groin

[DokterVet]

I'd say the bridge, followed by the shrimp, the shoulder roll and the wrestler's switch.

[KNOCKuOUT]

I would go with 7 swords (a variation know as 5 swords to American kenpo artists). Mutiple strikes in rapid fire to overwhelm the opponent.

[IKyokushinO-4]

Kyokushin - Gedan Mawashi Geri

[NightOwl]

Jab- annoying and helps you keep your distance

[Mistassailant5]

Phoenix Eye Punch.

[JiuJitsuNation]

Knee in the belly! The look on their face is classic.

[JAKEHE3078]

Shotokan - yori ashi gyaku tsuki (lunging rear hand punch) - it's almost a karate trademark and very distinctive.

I agree with this as far as karate goes, a direct, penetrating and powerful technique if mastered.

Ditto

[Cable Dog]

Soto-uke. Outside block. I can't remember how many times this basic technique has allowed me to evade a technique or even open a hole in someone's defense, or been used as my "secret" technique to use as an attack itself.

But truly, my technique of choice is Evasion. Dodge, then run away. No point in fighting in the first place.

[Groinstrike]

Kick to the groin, accompanied with simultaneous eye gouge