There is plenty of social networking websites but which one is the best social networking website.   

Agree with you. What is best for Mr A might not be best for Mr B, it depends on your objective.
What do you want to achieve?

As Mr Perfect said, what you want will determine social network that is best for you.

it's how effective you use each in my opinion. I am not on linkedin even though i've heard great things about it . Facebook and twitter does it for me. They both have their advantages so i dont really know which one to pick as THE social networking website but it seems facebook has a lot of reach than any out there tho.