If you have the new listing up and running before anywhere else, such as the MLS, your buyers can see the info when you are still processing the paperwork. It's a great tool. Use it to your benefit. It's also a great close at a listing presentation to already have it on your site. The most used search engine currently is Yahoo with 150 million page views per day.
Surveys show that people online tend to stay with the same search engines.
If they don't find what they are looking for, they are more likely to refine their keyword phrase then they are to go to another search engine. All of the major search engines get a sufficient amount of action or visits to make it worth your while to try to get a high ranking on as many as you can. Once you have your site, you have to look at it occasionally and make sure that the information on it is accurate. You should be reviewing the information at least once a week. You can't just create a web site and then leave it alone and hope that it brings in results.