Graphs and charts are a staple in multimedia stories, and for good reason. They allow the reader to both quantify and visualize the information at hand. However, in an ideal world, they merely complement and support the remainder of the story, so simplicity is key.
This is why the top graph would be more effective in a story than the bottom graph. Understanding of the point in the top graph—that Facebook has a much larger user base—can be reached in a second or two. The bottom graph, meanwhile, will take longer to sift through, because there is much more information and the unconventional presentation is distracting.
If one wanted to take the time and learn about the popularity of lots of different networks, then he or she would find the bottom graph quite helpful, but in general, the top graph will keep the reader going with the rest of the story.