That's a million dollar question that everyone who is trying to drive traffic to their site will ask at one point or another.
The short answer is that they're all different and each one has its strengths.
Chris Coyier posts regularly on several different platforms. In a recent article, he ran some tests in an attempt to determine which provided the best results.
Read the results of his experiments here.
As a little experiment, I shared a development tip on three different social networks. I also tried to post it in a format that was most suitable for that particular social network.