90%+ have come from my own sales sites since 2003. This provides me name,email, phone, ip etc... which helps in negotiations instead of blind negotiations from third party markets. Zero commission sales or Escrow fees helps as well.
If you have enough domains to do your own thing and are in this for the long haul that's the way to go. If you don't have enough domains to justify your own market I'd say Afternic has the strongest distribution path.
https://www.afternic.com/domain-reseller-network