Some points on here that I think are worth repeating:
1) Focusing on a particular style is a bad way to pick a school. It could well be Krav Maga is the best fit for you style-wise, but if the local school sucks, you are better off somewhere else.
2) The quality of the instructor and the focus of the instruction are better criterion. You want to learn to defend yourself and stay in shape. If the focus of the instructor is not self defense and fitness, you are in the wrong place. Also, you will run into a lot of schools that focus on fitness to the exclusion of all else (cardio karate and the like). So you want to be careful that emphasis is also put on practical applications of techniques.
3) The quality of the students is also incredibly important. If you ever have sparring drills you are relying on their skills to help you hone your own. Also, before sparring with anyone you have to be able to trust them. If you don't trust your fellow students why would you put yourself in a position where they can attack you?
My advice is that you should go to a number of the local schools, watch a couple of classes and see what each is all about. You should be able to narrow it down to a couple fairly quickly. See if you can audit a class or two, and you should be able to pick a school at that point.
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