Each social media has it purpose and target audience... LinkedIn is very popular for business people / professionals or those who are seeking for a job...
On the other hand, for example in Serbia, Belgrade, according to some of our research among students (not so big sample), the most popular / frequently used social media is Instagram, than Facebook.
Can't stand Facebook. I cannot see the point of it and rarely use it. I sometimes employ twitter to send messages. I mainly, when I have to, use linkedin. Like here, it provides debate forums.
Agree with colleagues saying that it depends on personality and region.
An interesting research to be carried out is the relation between age, or region, or personality, or education level, or gender, on the preferability of a social medium than another !