PPC is much more popular and in my experience easier to implement compared to an
successful affiliate program.
However, basic PPC setup getting simpler by the day has led to more and more people using it. This has led to inflationary pressures, with cost per click more than doubling in a very short period of time. This means that a lot of profit margins have shrunk. Further, you have to take into account that a lot of people bid with a view of getting traffic and exhausting their monthly budgets. A lot of businesses still have no accurate way of measuring ROI for each PPC campaign. Hence, the bids are sometimes too high, and outbidding these guys makes no sense from a business perspective. This leads to lower positions, which in turn will affect the total traffic that one can get now compared to a year back for the same budget.
In contrast, an affiliate marketing program, though tougher and more complex to setup and run, can be a very profitable exercise if the merchant manages to identify and sign up some good affiliates. It can be a big win win for both, the merchant and the publishers, if the right commission is offered for products. From a merchant's angle, he knows that he is only going to pay a percentage of his profits per conversion instead of paying for every click.
In fact, I had written a blog post on
Affiliate Marketing versus PPC a few months back.
Vishal.