None of them identify themselves as 'biased' afaik. They claim a particular 'perspective'. That's a much more neutral word, and they use it (or various synonyms) to give themselves credibility.

As you know, Fox calls itself 'fair and balanced'. If Fox (or MSNBC) changed their named from Fox News to Fox Propaganda Report with the tagline 'unfair and biased' then I'll accept that they are being open about their bias.