CNN was between balanced and slightly left back when it was owned by Ted Turner. Not anymore. They lean right. Look at their anchors political leanings: Wolf Blitzer, Anderson Cooper, John King, all Rebublican.
FOX has always been far right.
Dont know about NBC but MSNBC leans left.
The political leaning is irrelevant. All American media is owned by five corporations:
News Corporation (Murdoch)
Walt Disney Co (Owns ABC and all the "family friendly" channels)
The corporations' subsidiaries (Fox, NBC, etc) portray an "extremist" view of the news because it combats opposing corporations. To the corporations, it's not about the news at all: it's about marketing to an untapped demographic of US citizens to make the most money possible.
For real news, you must look outside of the US.
FOX -- extreme right wing, essentially a mouthpiece for their owner
CNN -- generally moderate, which causes the Right to call them liberal. Closest we have to the old Edward R. Murrow/Walter Cronkite ideal of responsible journalism
MSNBC -- moderately left-wing
PACIFICA RADIO -- only truly Left wing media I know of in the USA
BROADCAST NETWORKS -- no opinion because I haven't watched network news for years, except for local weather updates
WEATHER CHANNEL -- obviously extreme left-wing because they believe in climate change
CNN- Moderate left, always has a dem and republican during debates. Their pundits are pleasant enough and calm when compared to Fox. Generally left leaning but more moderate than fox. Tries to explain and inform rather than scare and confuse. More reliable and usually can back up it's points very well without any sort of double standard or "anonymous sources"
FOX- Far right, responsible for almost all misquotations, out of context statements, rumors, allegations, and generally a whole lot of propaganda and fearmongering. This channel continues to harp on Obama supposedly being muslim, a socialist, and not a citizen.
NBC I don't watch.