Which PPC platform is best for Network Marketing?

For network marketers using pay-per-click (PPC) as a marketing tool to get prospects for their businesses, one should consider the benefits that each platform has to offer as opposed to the cost of each. As of this writing, the three biggest PPC platforms available for use are MSN adCenter, Yahoo! Search Marketing, Google Adwords. Please note that not all of these platforms are built alike.

Of the three platforms, Microsoft