If I had to pick only one self-defense for a woman to learn, I would have to say jiu-jitsu. Now, let me be clear, I don’t believe jiu-jitsu is an all-encompassing martial art, but jiu-jitsu focuses mainly on how a smaller opponent can defeat a larger assailant through joint-locks, control and chokes.
In other words, let’s paint a ugly picture: Rapist-demon-spawn attacks you. He’s bigger than you, so his chances of getting you to the ground are a lot greater than you can probably imagine. Maybe you can get away, but a open hand shot to the throat, raking the eyes, and a groin shot SIMPLY DON’T CUT IT. Don’t be fooled into thinking pepper spray will do the trick either, it doesn’t, if a larger man wants to get you to the ground these techniques don’t work. However, any decent Jiu-Jitsu school will teach you (as a 100 pound girl) to kill a 300 lbs rapist. So, jerk-mcgoo goes to take your paints off, well, if you’ve learned some jiu jitsu, you’d know that he’s left himself awfully vulnerable for a triangle-choke, omaplata, or arm-bar.
But jiu jitsu is NOT all encompassing, for that, I put a pretty heavy emphasis on using the Martial Arts that have proven effective in the UFC. In my opinion, all martial arts have a place in the world, but because I fight professionally, I feel I need to be versed in the hand-to-hand combat that has proven most effective amongst professionals.
These are most typically:
Brazilian jiu-jitsu: The art of submitting your opponent through chokes and joint locks
Muay Thai: "The art of eight points", de facto striking technique of the UFC, utilizes striking with fists, feet, knees and elbows, while also utilizing clinch work
Wrestling/Judo: The art of controlling your opponent through superior positioning
There is a reason these disciplines have proven most effective at the professional MMA level. Other martial arts are okay to try, but I would stick to the martial arts that the professionals use.
Most cities have MMA gyms that train pro fighters, if you're ever in Salt Lake City, UT, I'd check out Factum CrossFit and MMA.