What is most watched 24 hours news channel in the usa ?

One of the first two but NOT the last one.

Yeah, we don't get Aljazeera in the States. I'd say it's probably split down the middle for CNN and Fox News. I don't have anything to cite that other than personal experience of going into people's homes to fix/setup TVs and I'd say it's split pretty closely down the middle as far as which network they have their TV tuned to (it usually has to do with their political affiliation -- conservatives tend to watch Fox, liberals CNN).