Here's what I can say, and it's not a personal opinion, but a common fact: PPC brings results fast, but you have to pay all the time. The sums get rather big. And you never know for sure, whether PPC will pay for itself, or it's just money down the drain.
SEO is different, in terms of investment and effect. First you pay (and all of us SEOs know that real optimization costs are very small), and some months later you start getting dramatic results. Yes, SEO pays for itself hundreds of times better, in the long run.
The amount of traffic that SEO will bring you is unlimited. You'd simply go bankrupt trying to get as many visitors with PPC campaigns.
This is a graphical representation of how it works.
SEO Certification
