As a 2nd deg TKD (Jon-ji school) stylist, I will give my take on this subject...
If you are looking to learn how to end a fight in the quickest, most painful, and most disabling to your opponent, learn Krav Maga or any similar. There are no intellectual challenges about life and philosophies in these teachings and I do not want to call them 'arts' even in the most generous definition. They are exactly that -- end the fight quickly with the most disabling technique to your opponent at your most opportune opening.
If you are looking for basic fighting techniques to fend off an opponent or perhaps even to put him down, then take up boxing. Between a Golden Gloves caliber fighter and a dan of any Asian martial arts, I will put my money on the boxer and odds are very very good that I will collect. Five-nines (%99.999) of Asian martial arts schools and instructors out there do not know how to teach combination punches techniques. Five-nines of kicks to the torso can be protected by a boxer's elbows. Boxers know how to dance with their feet better than five-nines of black belts of any Karate or TKD derivatives. I do not care what the movies shows, any punch to the head will reel a person and boxers are well trained to follow up once a punch connect.
Learn knife fighting techniques and carry a folding knife of at least 3-in blade. Not one of those Swiss contraptions. Learn 'weak hand' techniques.
If possible, learn escrima. A good beating with a stick will discourage an opponent without crippling him. The goal here is to extend your reach and a stick will allow that. A stick extend your reach while a knife increases your 'close-in' lethality. After one year of escrima training, if possible learn the bokken, the Japanese wooden practice sword. It is a weapon in its own right.