Depends on the product or service that I promote and if I am creating niche sites. Only two main concerns for me when doing keyword research:
1. Competition.
2. Keyword weight.
About competition. Before I do any keyword research I screen the competition for my product/service or niche site.
About keyword weight. Where the competition is overwhelming for the keywords (not worth my investment to compete) I move towards low competition investments and target keywords with low weight, phrases, and longtail keywords.
To be honest, I am a partner with someone who is considered one of the top ten
SEO/Keyword Specialists in Internet Marketing. I give her a niche topic and in 15 minutes or less she gives me a keyword report. But, the keywords we choose are based on the two concerns outline above.
It does not stop there. Backlinks to a keyword rich site (regardless of the keyword weight) do more for Google Pagerank than keywords alone.
In a nut shell:
keywords > backlinks > quality content = Good Google Pagerank
Jeffery 100% :-)