Realtor.com is the only “Market” platform. It is the official public facing display of the MLS. Once a listing goes live on the MLS, it is automatically pulled onto the syndicator platforms.
It has approximately 15% of the market for total home searches.
Note: if you pay for a flat-fee listing to get on the MLS, make sure your flat-fee listing broker can list for your specific area. The MLS is broken up into over 500 local databases. Does that make any sense? No. But it is a legacy system, and do not expect it to change any time soon.
Here are are the Syndicator Platforms. Here are the Independent Platforms.