The advantage to the internet (not just bloggers) as a source is the huge range of sources available. The mainstream media is extremely "inbred," or self-referencing--many major stories you see in local papers are just reprints from very few sources like the Washington Post or the New York Times. Often even broadcast news pulls their stories from these same sources.

The internet has a much higher potential for self-correction. Stories that appear there are immediately judged by many other sites, each hoping to be the one to score points by finding mistakes. In other words, they do the same thing to each other they do to the mainstream media. You don't see this as often in the mainstream media. Try to remember the last time the Washington Post did a "gotcha" on the New York Times.

Of course, all the advantages of the internet assumes you are smart enough not to limit yourself to only a few websites, particularly only the polemic ones. If you do that, you are just moving from one echo chamber to another.

Another advantage to the internet is that it provides easy access to a wide range of original material and baseline sources, something that was often impossible in the days before the net. This makes checking both mainstream news stories and internet stories easier. The best internet sources liberally link to the original material, research, and archives used to write their stories. I don't see this as often in the mainstream news, although they're getting better at it.