My hobby is boxing. It's always done the job on the few occasions that things have got out of hand but I do all I can to avoid getting into fights because I don't want a police record and I'm more or less guaranteed to break my hands which puts me out of training.

I don't think people need to worry about which discipline to pick because usually the person with the most training and sparring will be the better fighter no matter the discipline. If I had to pick though I'd say Muay Thai would be one of the best things to learn for street fighting as you've got clinching, elbows, and knees for close range, punches and knees for mid range, and the jab and kicks for long range (low kicks I guess as you can hardly do high kicks in jeans etc).

That said I think the best strikers in the world are boxers and if you asked me who I'd least like to get into a fight with then it would be a decent boxer. I don't really need to worry about that though because I've found in general that the discipline and strength of character needed to get good at a fighting sport means that most good fighters are very decent people.