Recently there was a question posted on LinkedIn:
If you were spending $10,000 on PPC and getting back $12,000 of turnover (making $2,000 profit), and spending $1,000 on SEO and social media and making $3,000 of turnover from google natural search, FB/Tw etc, where would you concentrate your efforts next?
I don't think it's possible, as far as the web has advanced, to focus all your marketing efforts in one basket. Today it's important to use a strategic balance of SEO, PPC and Social Media.
SEO is always going to be important because organic conversions always cost less than just about anything else you might do to bring in more business. With the emphasis on quality content, it's easier to target the right prospects with the right key terms.
While there is plenty of evidence that organic searches produce higher conversions than PPC but the PPC model puts your name up there for more impressions / exposure. You might pay for each click but the number of impressions your business will get between clicks is a vital part of any brand promotion strategy.
The social segment is necessary to create the "buzz" so people will refer your offering to others - because 78% of people make buying decisions based on what they are told by others. Using the big 5: Pinterest, Facebook, Twitter, LinkedIn & Google+, you can be fairly certain you'll hit your target in one, if not several places. Again this goes to branding and catching the person when they are ready to make a purchase decision.
So I would say to create a strategic campaign based on the proportion return you have been getting from each channel so far and test to find out which balance of your current strategy and new channels will give you the highest return overall.