For some reason, most of the time Google adwords is the only PPC method you are directed to: 8 or 9 to one ratio at least. I can not fully explain this one. There are a lot of adwords related products to promote as an affiliate and perhaps that's why they are always at the top of mind for most marketers. Yes, Google can usually send you the most traffic. So what, it's ROI (return on investment) we must be concerned with. Testing is the only way to develop profitable campaigns. Adwords has by far the steepest learning curve, and is much too risky for most of us. This is the fastest way to go broke unless you really know what you are doing. I am not saying never use them, I am saying be very careful. If you chose to buy traffic, there are a lot of other choices. Aside from Yahoo search marketing and Bing, here is a list of the top 50 alternate sources of advertising:
http://www.websitemagazine.com/content/blogs/posts/pages/web-rankings-top-50-alternativeadvertising-marketplaces.aspx