sedo & namedrive use a google ad feed and parked uses a yahoo ad feed, parked allows you to add titles, meta tags and custom content where the other 2 don't, bottom line is revenue so put your domains at a provider for a month then switch and when your test is over move each domain to where it makes the most income per month, ignore pay per click, click through rate etc... as nobody counts it the same way, bottom line is revenue per month, a few companies I have used and what feeds they run...
Google= sedo, namedrive, fabulous, domain sponsor
Yahoo= parked, trafficZ, smartname