Hello,
Yahoo holds the largest market share (because more searches are done there, because you don't always get what you want firsdt time so you search again) But Google is the most popular because they get you what you want first time. Listing with search engines is very important but you need to make sure your web site is "search engine freindly". This is done by making sure your key words are relevant to your site, Google looks for a minimum of 200 links to your site (not 200 links on your site) as a way to increase your listing. Google figures if 200 sites link to yours then your site must be good and they rank you higher. Your key word must be in your title and you must use your key words at least 6 times in the texct on your index page. I could go on.
Hope this helps.