Keyword Research And Analysis, comprehensive keyword analysis @ depth

We all use many tools and resources to get the keywords for our web site optimization. But are we really sure that these tools and resources provide the complete information and that too accurate?

I think the best way to have a fair decision in finding and finalizing the keyword is to - collect the data available from the tools and resources, then compare all this across factors and then make a decision judgement based on the conclusion you derive from these reports. Is this the ideal way to carry out the keyword research and analysis?

Also one should not depend on one tool or resource to make decisions for keyword selections. Right?

Although there is no clinical proven formula for keyword analysis, so which resources and tools will be more useful, I mean the third party tools or the one provided by search engines itself?

I personally think the best method is a cross between using the search engine resources and your own opinion.