I practice amateur boxing (more like a simple enthusiast). I choose boxing over others because it was relatively simpler, but also because it is less violent. In fact, it is an olimpic sport. MMA and others are also quite technical, mainly due to jiu-jitsu usage, which decides many fights, but they are also far more dangerous if you want to be serious and fight occasionally.
Of course, it depends a lot on personal preferences too. Some friends of mine say that boxing is too quiet. They prefer to be rolling on the ground trying to immobilize the opponent. For personal defense, it is essential. But just to practice a sport, I personally don't like MMA.
Other really interesting types of fight are muay thai and kick boxing. They will train the whole body, which is always good. Kicks are really powerful, both in fights and in self-defense.