The debate between SEO and PPC has been going on for a long time, but have you ever thought about it from the angle of traffic? There are merits to both of these online marketing strategies and most people get the best results from combining them together, but you could argue that SEO traffic is better than the traffic won over with PPC.
Think of how visitors find your website through optimization efforts. You target the same keywords they are typing into the search engines while building your reputation with the top search engines. You therefore become a natural recommendation from the search engines to those looking for information and products. You appear in the SERPs because you are considered a valuable website offering exactly what these searchers are looking for.
Now think about how your website is found through pay per click advertising. You are on the SERPs, but not as a natural recommendation and not because you have established a top ranking reputation with the search engines. You show up in a specially designated area that many people know is for paid links put up for advertising purposes.
When you take action to draw in SEO traffic you are also advertising, but many searchers don't understand how specific websites are recommended to them. They just know that the ones on the top and along the side are advertisements while the ones on the main list are in order of value. They go for those on the top of that list believing they are the best sites or most reputable sites.
SEO traffic relies upon that belief, even if it does not always hold true. If the best sites that offer the most valuable information end up on top and your website hits the top, then you get lots of clicks. You get lots of SEO traffic from people interested in exactly what you have to offer. It doesn't get any better than that.