The best answer to this is to say that the most effective leaders use all of the styles of leadership.  A leader who is one-dimensional and can only use one style of leadership is most likely to be effective only in a limited set of circumstances.  Empirical research has shown that different styles of leadership work better in different situations.  

For example, when a business or an organization needs to be taken in a new direction, the best kind of leadership is visionary leadership.  When an organization has been demoralized and the people in that organization do not trust one another, it is best to have an affiliative leader who can start to patch things up and get the employees to work well together again.  An authoritarian style of leadership is only really effective during times of crisis.  

In other words, there is no one style of leadership that is best.  The most effective leaders are those who can understand which style is needed at any given time and can effectively deploy the proper style.

What style of leadership is the most effective in leading an organization?

The best leadership style can be described as no leadership style.  Alternatively, it can be described as every leadership style.  In other words, the best leaders are leaders who can use all of the leadership styles.  They are not wedded to any one style.

The reason for this is that research shows that there is no one leadership style that is always the best style.  Leading a business is an extremely complex task with many different challenges that arise on a consistent basis.  Since the situations that leaders must deal with can be so fluid and so different, the best leaders must also be fluid and adaptable.

This means that leaders must be able to use each leadership style when it is most appropriate.  They must be able to be authoritarian when important decisions must be made quickly.  They must be able to be more inclusive and allow their staff to feel that their input is valued in instances where a variety of viewpoints can be useful.  There is no one style that is always the best, therefore, the best leaders have all the styles and are not simply wedded to one.