In terms of time versus result I would just say Jiu Jitsu.
The reason for this is because jiu jitsu is rooted in concepts. Concepts of position, position transitions, and control positions. These concepts, once learned, are not unlearned. They don't require the flexibility needed for a head kick or the extensive repetition of refinement needed for kickboxing, boxing, taekwondo, etc.
Give a person a 1 week clinic in jiu jitsu and they can literally learn techniques needed to survive an attack from an average person, long enough for help to arrive.
Thankfully, most of these concepts have been around in other martial arts or have spread to other martial arts within the past 20 years. Pretty much any Jiu Jitsu gym teaches this basic stuff.
The reason for this is because jiu jitsu is rooted in concepts. Concepts of position, position transitions, and control positions. These concepts, once learned, are not unlearned. They don't require the flexibility needed for a head kick or the extensive repetition of refinement needed for kickboxing, boxing, taekwondo, etc.
Give a person a 1 week clinic in jiu jitsu and they can literally learn techniques needed to survive an attack from an average person, long enough for help to arrive.
Thankfully, most of these concepts have been around in other martial arts or have spread to other martial arts within the past 20 years. Pretty much any Jiu Jitsu gym teaches this basic stuff.