Google vs. Yahoo - Search Engine Differences
Because different Search Engines use different algorithms, your web-site will never have same position in different search engines, no matter how optimized it is. The question is, for what search engine should you target optimization?
Google, Yahoo, MSN, AllTheWeb, Altavista, or some other?
One way to decide is to know what search engines have most users. Those are Google and Yahoo. However, these two give very different results. Which one is better? Well, experience tells it is Google, and for several reasons. When typing a 4 word query that exactly matches a (good) page on one web-site, and gives a total of only 40 results, Google gives the right page, while Yahoo gives several wrong pages that link to the right page. This is only one obvious example that tells with certainty that Google algorithm works better.
Google algorithm is more democratic. This means that new pages and web-sites can more easily compete with old and well established web pages. For Google, content is more important than links and site history. Yahoo seems to have an opposite approach. This is an obvious reason to choose Google, as content can be changed, history cannot. Also, since the number of new websites is expanding every day, new site owners will like to see their sites in search engine results, and since this is more probable with Google, you can bet that Google will have more and more users, and Yahoo will have less and less.
As a conclusion, while most engines have some things in common, and therefore some search engine optimizations will be useful for all, in some aspects they rank results very differently, and therefore, what is better for one engine is worse for another. This can be made an advantage, if for example website SEO achieves top results for different variations of a phrase in different engines.
Note that if you are in a competitive industry, optimization for multiple search engines is possible with technique called cloaking. Cloaking means that different pages are shown to users and to search engines. In addition, each search engine can be served with a different page, but this requires additional investment. Also, it needs to be done ethically, as providing one page to users and significantly different to search engines would be misleading for users, and would get your site on a black list (banned). Ethical means, for example, providing some text in bold to one search engine and in italic to another because each may like better bold or italic.