i have trained 3 different martial arts styles and the best one that resulted in street fighting is the Ken arts. Besides that i have trained traditional karate style and tai-chi-chuan and they didn't help so much as the Ken style. It is a dynamic style that can be used anywhere you want to fight.
Well there is no " most effective" but if i were to choose i would choose 2, muay thai & bjj. why? cause one is for striking and the other for grappling, but if u need one for self defense take krav maga. Hope i helped.