Let me add this.
I have shot with people who shoot USPSA and consider it ample training for a defensive encounter (to which I laugh at). They think that because USPSA teaches you to "double tap", it is all you need as far as training goes. The problem with USPSA is that you can miss fast enough to win, because accuracy is not weighted as heavily as it could be.
However, USPSA is not bad by any means; it can be a great supplement to defensive training. It gets your heartbeat going, some adrenaline pumping, and it makes you think. It does test accuracy to an extent, but it does not test defensive tactics.
Now, while you can miss fast enough to win in USPSA, misses don't get you anything in a firefight. On the flip-side, USPSA does help because it teaches you to shoot quickly under some stress. There are people who only shoot at a range and think that is plenty. For them I say; you can hit slow enough to lose. A hit that you have to take too much time to line up can get you killed just as fast as 3 shots that you fire too quickly and don't aim well enough.
Basically, get some actual defensive training, and then find something to supplement it and keep your skills sharp (aside from range time). IDPA is another good one, and it is focused more on defensive tactics.