After reading the article by Yukl it's clear to see that no matter how much research is done, there is still always room for more research on Effective Leadership Behavior. There's so many traits and behaviors that a good leader should possess that you can't narrow it down to just one.
"This pattern of results suggests the possibility of a curvilinear relationship such that satisfaction is highest for a leader who uses a moderate amount of task-oriented behavior." You need to have a mix of qualities and behaviors in order to be a great leader and for me, having a supportive leadership style is extremely important.
"“The moment you feel the need to tightly manage someone, you’ve made a hiring mistake. The best people don’t need to be managed. Guided, taught, led–yes. But not tightly managed.” -Jim Collins
You need to be able to bring out the best in people and encourage them continuously, so they not only strive to be good, but to be great! His book "Good to Great" tells about his views and thoughts on what he calls Level 5 Leadership, which has a mixture of professional will, and personal humility and the level at which you are at.
"Level 5 Executive -- builds enduring greatness through a paradoxical blend of personal humility and professional will
Effective Leader -- catalyzes commitment to and vigorous pursuit of a clear and compelling vision, stimulating higher performance standards.
Competent Manager -- organizes people and resources toward the effective and efficient pursuit of predetermined objectives.
Contributing Team Member -- contributes individual capabilities to the achievement of group objectives and works effectively with others in a group setting.
Highly Capable Individual -- Makes productive contributions through talent, knowledge, skills, and good work habits."