One of the craziest truths about self-defense is really how much being in some sort of shape plays into it. Now obviously, training seriously in wrestling or grappling will put you in great shape. The oddity is that most people who actually train seriously are never really the aggressors. And most aggressors, at least in my experience are never really in that great of shape or are drunk. This is where fitness plays a role because after that initial 40 seconds, the other guy is winded and you are still fresh and have some skill.
So the first rule of self-defense is to get into shape. Then you can pick a style that suits you. Some are better than others depending on the application. BJJ, Boxing, Wrestling, Judo, and Muy Thai have been proven to be extremely effective. Krav Maga and FMA are also good. TMA can also be effective depending on techniques. But all are way more effective when the practitioner is also fit.