The difference between DomainSponsor and Sedo is that DS does pay for traffic as well as clicks, which can be significant if you have a really high traffic domain ($2/1000). They seem to have a bit less CTR though than Sedo does, but the ads pay better per click. DS, unlike Sedo, requires a certain qualified domain portfolio and you have to be accepted there. Fabulous, which is like DS, has a 100 domain minimum or if you have less and high quality traffic domains, they might let you in with that. Sedo doesn't require any minimum or really much of anything to join. I haven't tried NameDrive, will look into that. Sedo has a min payment of $20, DS has a min payment of $50.
Most money made, unless you have a really high end traffic domain, is development and then perhaps Google or YPN ads, rather than parking, but it never hurts to keep them there and make a couple extra bucks while you are waiting to do something with them.