It depends on what you want to do.
I use twitter and Linkedin for reach. They both work well when it comes to reaching the broadest group of my followers with images and text. Facebook probably has the best platform for hosting images but reach has been a question mark for me especially for large audiences and fan pages. Compared to Facebook posts, Linkedin groups have given me significantly better results.
I like how boards are organized over at Pinterest and how easy it is to aim at a given key word. But my challenge with Pinterst, Stumbleupon and Tumblr has been the same. I have yet to figure out the right process for generating traction and coverage on them.