Marketing, advertising and public relations firms have all changed in the past decade. So how do I know which to choose?

The difference among marketing, public relations and advertising agencies was, at one time, significant. Long before digital marketing dominated the industry, marketing firms focused on basic awareness tactics, such as direct mail, newspaper inserts and flyers. Advertising agencies used to focus on things like television, radio and billboard ads. While public relations firms helped clients appear in media stories. All of these approaches were designed to increase awareness for their clients and hopefully drive sales.

But that’s all changed. Old marketing channels have shifted to social media. Television and radio have moved to YouTube and Pandora, while public relations has become mostly content marketing. All told, these three distinctly different industries are quickly merging into one — creating client-focused content that is communicated through a myriad of digital and traditional channels. For instance, a single blog post about what makes a golf ball fly farther is great content for Titleist to repurpose in many ways. They can post it on social media, their web site, send email blasts, optimize it for Google search, digital display ads, brochures, Golf Digest magazine, YouTube and a host of other venues.

The three practices traditionally grouped under the umbrella of “marketing” have all merged into what is commonly referred to as content marketing. So, which agency should you choose? Because most agencies now are content development firms, the answer lies in who is best equipped to create and disseminate the type of message that is right for your brand. Large consumer brands still gravitate toward the old ad agency model, because they tend to know how treat consumer marketing well. The old marketing firm model has morphed into digital marketing firms, usually comprised of tech experts focused on deploying digital messages. These agencies know the technology well, but aren’t always the best writers and content developers. Meanwhile, the companies that grew out of public relations, were originally built on writers and content development. Media relations experts are often former reporters and journalists — the people who studied and were trained to develop premium content.

Most of these business models have adopted well to the expertise of the others, with one ironic exception: Digital marketing firms today are typically comprised of tech experts who know little to nothing about writing, message development and branding. To them, the focus lies deep within the analytics, such as how to optimize digital exposure and maximize clicks and spend efficiency. The content producers from PR firms will argue that none of that matters if you have the wrong message and appeal to the wrong audience. The ad agency folks will content that without highly creative material, your audience won’t notice, and the digital folks claim the others don’t really know the technology.

The truth: They’re all party right, and they’re all partly wrong. Digital agencies can hire great writers, and PR firms can hire digital techies. And both of them can hire creative ad gurus. It all depends on where you want to focus your marketing efforts. Ad firms typically charge premium fees for their creative expertise, and digital firms charge by the number of people they engage. Public relations firms charge by the hour, and marketing firms are somewhere in between.

If you’re exclusively an online business, start with a digital firm. Large consumer brands should move to the ad agency model, and most other companies and non-profits will do well with marketing and PR firms, which offer hybrid approaches.