I took a different approach to this than some might. Rather than choose the zips I know to be saturated with REOs (and agents), I went with some outlying zips. These aren't rural, just in surrounding suburbs.
I figured most AMs would already have their chosen agents in the popular zips but might not be familiar with anyone in some of the less popular zips. To me, the ads are really just an opportunity to get your foot in the door with some new companies and build new relationships. If AMs already have preferred agents, there's no need to click on your ad.