Revenuedirect has the biggest payouts per click, they just have a hard time paying you on time. So if getting paid 3 weeks +/- late will hurt you then stay away from revenuedirect.
Sedo I think converts poorly except for domains that get more foreign traffic. payout rev per click is moderate.
Fabulous.com has the lowest and worst payouts - they most likely take the biggest slice of pie of your earned revenue from your domains and conversions stink.
Whypark is cool cause they allow you to use your own sponsors and keep 100%, but they dont have articles for all online niches. Once a park site gets picked up by a search engine good CTR, just takesa few moths.
My favorite is
Parked.com, they have impeckable customer service. 90% of my
parked domains are with them. They have the next highest payout behind revenuedirect, but only by a few cents. They always pay on time. Which is worth a lot to me. They are adding some cool new UI's as we speak to admin panel.
Best of all they allow you to modify the footer, now they have an easy to use wysywig. You can do cool things with a parked.com site.
Example:
Heres one of DotComGod's (Adam Dicker):
Download.net
Couple of mine - Keyword2myurl.com, yotd.net, acttconsult.com
This is my expierence testing the same handfull of domains at each provider for 2 - 3 months each. The domain niche was credit card, loans, and payday.