Bloggers gravitate toward stories (often political) that elicit emotion. Twitter is squarely focused on technology. YouTube, while its top story was often seemingly random, has social media's most international mix of stories.The full report is here. And even more detailed one about blogs is here.
Blogs were most like the mainstream media, followed by Twitter and then YouTube. Keep in mind these are broad categories, such as "health and medicine" or "politics/government," not specific stuff like Dancing with American Idol or similar crud, so there's plenty of room for agreement -- and, apparently, disagreement. Blogs focus more than the mainstream media on such topics as science and technology, while the evil MSM spends more time on health, medicine, and the economy.
Twitter, or rather those who use the site, is crazy about tech. Forty-three percent of tweets were about technology, suggested a lot of geeks talking to a lot of geeks. Apparently no one on Twitter worries about the economy (1 percent).