What type of fighting style is the best for street fighting?

What type of fighting style is the best for street fighting?
"Best" is always a matter of opinion. "Street fighting" is a term for real self defense. The actual location of the fight (on a street, in a building, in a field), might affect the particular strategy and tactics used, but there is no "best" fighting style, except to use whatever works at any given point in time and situation. Most legitimate systems of unarmed combat or self defense are designed to adapt to a variety of terrain, and circumstances. Some factors that limit success are those methods that focus primarily on grappling one on one, since "street fights" might involve multiple attackers.

There are no proven, or legitimate statistic as to what percentage of self defense encounters go to the ground, but all effective systems of training should involve techniques and tactics of how to maneuver, escape, and survive ground-fighting, and not necessarily prevail on the ground. Many striking systems are quite effective at preventing the opportunity to take the defender to the ground without being seriously injured or knocked out, and can utilize strikes and escapes to nullify ground-fighting tactics.

Also, many people are mislead by the MMA and cage fighting fads which are sports that have referees, follow rules, and disallow certain techniques. "Street Self Defense" has no restrictions on what can be done, and survival might require the use of deadly force. Any good system of self defense will contain a balance of striking, throwing, and grappling techniques that can be used at long range, medium range, and close range fighting. What tactics are applied in any given fight is up to the individual, and might prove to be successful or not depending on a great many factors.