Though they are the most expensive Overture provides the highest quality traffic.
Google Adwords are expensive and very difficult to administer but they probably are the second best out there. They are very frustrating to work with though as they have a tendency to exclude all the most desirable terms and deactivate the rest for low click thru rates, you then have to pay $5 to reactivate the words and they do the same game again to chisel another five bucks out of you. If you have a lot of patience and a stack of 5 dollar bills they can produce a few players.
At times Findwhat produces some results but their traffic is VERY spotty.
Most of the remaining PPCs are virtually worthless. You will get tons of clicks, but very few if any real depositing players.