Return On Investment
Search Engine Optimization (SEO) and Pay-Per-Click (PPC) are the two leading techniques in the Search Engine Marketer's (SEM) toolkit. While both are powerful strategies to increase website traffic, most SEM professionals who offer the two services agree that SEO earns substantially better ROI than PPC does.

Retail Marketplace
That does not mean PPC is not highly useful, or even preferable for some sites and businesses. If you are in the business-to-consumer (B2C) marketplace, keyword/phrase buys are typically required to sell your products and services online especially if you are in a competitive industry.

How End Users Search
On average, about 70% of click-throughs come from organic search results with studies showing conversion rates approximately 25% higher than PPC click-throughs. Here again wide variations are to be expected among different industries and between the B2B and B2C marketplaces.

SEO & PPC Programs
PPC campaigns are easier to set up and launch more quickly than the full optimization of your website even with the development of landing pages and managing multiple ads. The downside is you have recurring monthly keyword buys to budget for and the potential for click fraud.

Whereas SEO when done right, although a longer process, needs limited attention when complete and will definitely increase your keyword/phrase rankings against your competitors.

Which Program
As a short term strategy, pay-per-click has the advantage over SEO, but as a long term solution SEO provides the greatest R.O.I. for most companies. Even if you opt for PPC campaign, it is highly recommended to add organic search optimization to your marketing strategy.