It is increasingly becoming an irrelevant question – either/or. A few years ago you might have had a choice, but today your choice should be both. Promote online and offline.
Most shoppers these days begin their shopping online. Even if they purchase offline they are doing research online. That means the opportunities to touch your potential customer are manifold more than what they used to be. Before the Internet all you have was print advertising, TV, radio, and outdoor advertising. You have more options than that online today. Plus, there is mobile advertising, e-mail, etc.
The most effective advertising utilizes a mult-tiered approach that focuses on reaching the right audience with the right message. Don’t toss out a medium just because you don’t understand it or don’t see the need. Do some research and study the market then attack where your prospects are.