First, who's making the reccomendation? Someone associated with the parking co? How do we know for certain?
Second, portfolio quality affects results. You have prn traffic? Then parking co #7 works best. You have international traffic? Then parking co #3, 5 and 11 work best.
There are only a few major players, ones using a Google feed, and those players have gotten a bit more selective.
Everyone has a favorite. How do YOU or anyone else intelligently "find a favorite"? You do this by parking your domains with the different providers and seeing how their parking solution works for YOUR domain traffic.
It has ALWAYS been my advice to move your domains around to test the companies. That's the ONLY way to know whose solution is best for your domains.