I think it is a tie between their publishers or editors and the public. It should truly be the public but how can a journalist keep their job if they go against the superiors? It is most likely they would get fired. However they should have their first priority to inform the public. Again if they do not inform the public well enough they could lose their jobs.
They have to balance very carefully on a teeter-tater. They are in the middle and the public is on one side with the publishers and editors on the other. If one side is catered to more then the journalist crashes off.
Their loyalty is completely with the company or organization that hired them. Their goal is to inform people about the good sides of the company and not the bad. They must tell the truth about the company but maybe not all of the truth. They only have to tell the good truth and not the bad. They are on a merry-go-round of the company. It starts slow for them to get on but their information helps keep the company going and succeeding. If they do not keep total loyalty to their company and step a foot off the merry-go-round, they will fall off and probably lose their jobs.
It is different for journalists and PR practitioners. They have different loyalty dilemmas. I believe professional loyalty is important but not more than personal loyalty. For example, if a reporter writes something about a local political group that gets published. However, her editor took out some facts and quotes that would have made the politicians look good, what should she do? She has to be loyal to her editor or get fired but she believes more in the loyalty to inform the public of the truth to the best of her ability. She quit and will not work for her again. Luckily she had that option but journalists don't always.