That doesn't work either. One, there's the assumption that you're two opposed news sites are "really" opposed. Are Fox News and MSNBC diametrically opposed? Amy Goodman would disagree. I could also read the Socialist Worker Magazine and the American Enterprise Institute's newsletter, but I don't know what conclusions I would draw.
The issue isn't that all media organizations are biased, it's really that I am biased. I think the world exists in a certain way and the news that doesn't agree with that or fails to convince me to change the way I think, well then that news source is clearly biased.