Many a prospect has asked about how to find the best blend of marketing tools and practices. The real answer here lies in what is best fit for your target audience (which is quite often a mix of offline, digital and other media).
There are many agencies that specialise in digital, media planning, consultancy or one of a number of disciplines; the issue arising that they are but a colour (or two!) on the canvas which is your business. Knowing when to adopt an agency who sees the bigger picture can often be make or break on you seeing a return on investment.
So, with this in mind, research becomes key in understanding your markets. Look for an agency who will delve deeper into your respective industries to find untapped routes to market and how to best use both traditional and digital (new) media to your business advantage.
This is not to say however, that cases will not exist where this is not necessary (or even prudent) to do. Some services are so specific, and the market so narrow that there will sometimes only be a few viable options to promote yourselves. As always, contacting a professional and experienced agency for insight is often the time and money saver you need.