Its hype, all these websites look the same.
What i advise you to do is:
If you are a publisher, look at the Advertiser info. It will promise you the world of how you will get the best rates.
If you are an advertiser, see what they sell their publishers.
Its again hype!
A commenter above stated you are best off selling your own ad inventory.
What i suggest is you use a fixed price venue such as buysellads.com,
Keep track of what is being posted on your site (who buys ads)
Then sell to them direct!
CUT THE FAT, but once you recognize who will pay for your ads.