Journalists owe their loyalty to more than one group of people. They first owe it to their publishers and editors. It's hard to say this sometimes, but if a journalist loses his or her job, he or she also loses value as a means of communicating news to the public.
Second, journalists definitely owe their loyalty to the public. They owe them the duty of being fair and accurate. They owe the public the right to hear information for which they can process and learn from. Journalism is for the public; therefore, journalists owe loyalty to it.
I also think that journalists owe some loyalty to their sources. They must be loyal in that they correctly communicate the news from their sources to the public.
Public relations practitioners are in quite a different boat. Like journalists foremost owe loyalty to their publishers, PR practitioners owe it to their company. It's the company who is hiring them to make it look good- doing the job right does not always being staying fair and accurate.
Hopefully my professional values never conflict with my personal values. Loyalty ranks very high with both my professional values- I just hope I won't need to test my personal values in order to stay in my profession. I guess it all just depends on the situation.