Mulitple Terms in Multiple engines

[webmaster007]

Hello All! I have a question for all you gurus out there. I have various sites which I am trying to optimize. When looking through the 4 major engines (Google, Yahoo, Ask, MSN) I am noticing that any one site will do well in different engines for different keywords. My question is this...is it better to optimize a site for mulitple keywords in one engine, or is better to take advantage of current organic rankings by optimizing one site for different keywords on multiple engines. For example, if I have a site geared toward SEO and I notice that I rank #4 in Google for 'seo' and #5 for 'link building' in Yahoo but I am #75 for the term 'link building' in google and #30 for 'seo' in Yahoo, is it more beneficial for me to optimize my site for 'seo' and 'link building' in Yahoo or Google, or is it more beneficial for me to optimize my site for the term 'seo' in Google and the term 'link building' in Yahoo and hopefully gain a #1,2,3 position for both terms in separate engines? I hope this is not too confusing...any opinons, advice, expertise would be greatly appreciated. Thanks alot!