I have a deep abiding respect for the martial arts, and worked out in Tae Kwon Do for many years. Taught properly, and approached as more than just "learning how to fight," the discipline is of tremendous benefit to many physicsl, mental, and emotional aspects of one's life...as are many of the "classical" martial arts.
If one's goal is to quickly learn how to defend one's self in dangerous situations, which differs from the goal of learning a martial art, I'd suggest seeking out a course geared specifically to self-defense training. I say this because I had an eye-opening experience while sparring with several white belts during preparation for testing for one of my advancing belts. One of these newbies was an "untrained" fighter, which meant he didn't fight at all like a martial artist, but he had learned via the school of hard knocks on the street. Despite my years of training at that point, I really struggled against him, and learned a lot about what is useful....and what isn't in certain situations.
If true martial arts appeal to you AND you're interested in useful personal defense and control, I'd recommend Aikido and/or Jiu Jitsu. Neither will be a quick path, but the concepts of redirection and control, at least in my experience, are more useful than strikes and blocks....and result in less harm to all parties involved, unless of course harm is intended...and it shouldn't be.
Again, if you are looking for fast results and don't want to spend years training, a course geared specifically towards self-defense techniques may be more useful in the near future.
Just some thoughts. I am not, by any stretch, a master or expert.