What's the best martial art for self defence that's not necessarily lethal?

Well, muay thai has the leg kick, and so do other styles like Burmese boxing, Laotian boxing, Khmer boxing, Filipino kali, Kyokushinryu karate, etc. The leg kick is generally non lethal unless it makes your opponent throw a clot. But it is probably the single most effective technique in all of martial arts.