Jui-Jutsu or another "soft" martial art. Or, as has been said before, MMA.
Defending yourself in a fight is not about learning a single martial art, but rather having a toolbox of different skills in place to allow you to draw on the best one for the situation you are in. Just be aware that most fights finish on the floor quite quickly, so learning something that teaches how to cope with that is a good idea.
I did three years of TKD and it was great, but the year of ninjutsu I did after that was far more practical, well, the unarmed combat stuff anyway. I'm also lazy, so the idea of using an opponent's energy against them rather than doing all the kicking or punching made a lot more sense.