I think it must be between these three: CNN, ESPN and MTV.
CNN: Round the clock news coverage helped spawn an information society where it is better to get the story out quickly as opposed to correctly. Spawned MSNBC, FoxNews and created the blanket coverage of major events.
ESPN: Even if you don’t like sports it is almost impossible to ignore the prevalance of it in today’s society. And ESPN increased the exposure of athletes to the point where they are celebrities on par with the biggest moive stars.
MTV: Artistically MTV helped spawn a visual style that predominates TV, movies, and commercials today. Secondly it increased the influence of the younger generation. Thirdly, the growth of the “hip hop” nation can largely be attributed to MTV embracing the music and the lifestyle that it goes with it.
I’d narrow it down even further: CNN vs. MTV. Particularly when you’re talking worldwide, compared to just the United States.
When I saw the title, I immediately thought of MTV. I didn’t even think it would be close.
But the OP changed my mind. CNN definitely had the biggest influence. It changed the way the world is run.
MTV has been critical in the declawing and reselling of the grittier aspects of youth culture back to the general populace. The network has also increased the speed through which entertainment novelty is disseminated, pretty much eroding the time gap between urban and rural locales when it comes to fad adoption.
Also, with Real World, MTV has been largely responsible as the catalyst behind reality TV.
CNN’s contribution is more along the lines of info-glut and reliance on secondary scroll graphics, though those were already used to show financial information. CNN also pretty much ended the dominance of pre-cable network news as the prominent disseminator of current information on TV.
ESPN is certainly ubiquitous, but I don’t think it’s changed culture nearly to the extent of the other two.
Is ESPN truly responsible for that? It seems to me that a lot of athletes were already mega-celebrities, long before ESPN.