I would say that the true answer is that all can come out winners if they do the right moves and don't venture in to each others territory. Adverising is strongly connected with the economy and in the past 100 years there has been a steady growth in all markets.
Nowadays, even though internet advertising is on the rise there is still no shortage of demand for print and tv ads therefore ad agencies keep getting bigger. PR firms continue to do their part in pushing agendas and getting articles written about their clients. Marketing consulting is necessary for companies to know who not to trust and keep tabs of their efforts and digital agencies are ever growing along with the internet.
The only danger is that one of these parties will try to step in a territory they don't understand and fail miserably. What usually happens is that ad agencies form special digital advertising branches and pr firms hire internet age marketing consultants that help them branch out.
