What is the best martial art to defend my self in a street fight from one or more attackers?

I live in a rough city and im interested in starting some style of martial art to defend my self from gangs, p addicts and muggers etc. What would be the best fighting style (karate, muay thai, jujitsu,judo etc) to ensure i would be able to over power or knock out an attacker or a small group of attackers without myself being injured?