Much has been written about the subject, and the bottom line always seems to be the same: both technologies should be used as much as possible. SEO is better in the long term, and AdWords / PPC (pay-per-click) is more appropriate to get results quickly.
At the last convention of the SES (Search Engine Strategies) in Chicago, Michael Gray, and Christine Churchill had opposing views on this matter. Gray stated that Google is making changes that could affect the outcome of the ranking of organic positioning. One change is the recent introduction of personalized search for all Google users, for users authenticated through their Google Account to anonymous users (using cookies). Gray spoke about this and other changes.
Churchill defended the usefulness of the CFP for people starting to settle on the Web by themselves. The reality is that SEO require lot of time, and although it has great importance and is a significant long-term benefit is very difficult to be competitive. When starting with the launch of a new domain, a new site, and that has no link yet, always starts normally invest time in raising the ranking for a certain keywords. PPC allows you to do so while getting a good impact ROI (Return of Investment) quickly.
However, not everyone agrees with the PPC is the most suitable for a new website. SEO optimization is a requirement when dealing with new websites. No search engine will boost the ranking of a site in organic search for failure to comply with the recommendations of the search engine, and the results of organic search listings represent 24 hours of continuous, not being the case unless PPC invest a lot of the PPC budget.
PPC should be used after a good SEO optimization, to cover areas that can not be met by optimizing SEO. For example, a very good use of the PPC is to offer products or services in the short term, by SEO take long position in organic searches.
However, one thing to keep in mind is that PPC can be used to better determine the right direction for further optimization SEO. PPC can quickly use to determine which keywords best conversion factor and use these keywords in your SEO optimization, thus avoiding wasted effort in a SEO optimization for keywords with little or no conversion factor.