Dear Norchene, for personal contacts Facebook is my favorite and I believe also my country's favorite social media. It's free, it is there whenever you need it, it's reliable and it brings together people from all over the world. In the academic field, ResearchGate and Academia.edu (although the latter has recently started to be commercial) are by far the best platforms for scientists and the visibility of their work.

Best wishes!

 Thanks Hojjat Emami and Soultana Kapiki 

I think all depends on the aim you expect make from the use of each social network:

If you intend a social network for researchers and academic exchange, I think you are already on the right platform (i.e researchgate). Otherwise, for a manager, I would say that linkedin is far better (Despite here in France, professionals still prefer Viadeo and relatively Xing in Germany). Moreover, Twitter is considered to be the best SNS for sectorial monitoring besides the promotion of an event (conference with twitos in live). Otherwise, even if it is possible to exploit it professionally, personnaly I keep facebook for a familiar use with relatives, closed ties or coleagues that i have known since a long time

Social Media sometimes lead to addiction (eg Facebook). It is very important the type of Social Media that we choose and time devoted. It is important the purpose of choosing a certain type of Social Media. ResearchGate is a good option for dissemination of scientific papers and information.