I have been online for a while and had tried both of them. I will have to say that I had never had any success promoting offers with PPC. Also, these days, PPC is getting harder and harder for advertisers to get to. I had recently had my google adwords account suspended because of the fact that I was just an internet marketer just trying to make some money.
Anyhow, I recommend SEO. It takes a little bit longer before you start seeing results, however, if you do it smartly, you will be able to receive free targeted traffic. All of your sales will be a profit.
Doing SEO smartly basically requires for you to use google keyword tool and finding keywords with high search volume and little competition. Google keyword tool will show you both of these factors. You can also get a better idea on competition by simply typing in the keyword in quotation marks. If you see a result of less than 30k, you have a pretty good keyword as far as competition goes. Oh, you I recommend keywords that have a search volume of at least 5k a month.