As per my experience Google Keywords Tool is best tool. You can get all related and exact search results which are previously searched which can help you to write a SEO optimized article.
if you want traffic from Google use Google keywords tool ans if you want traffic also from Bing use Bing keywords tool also
There are so many out there. some of them are better than google keywords tool but they are not free. So personally I believe that google analytics is enough to research good keywords freely.
For a free tool you can try Google Adwords Keyword tool - it will give you a general idea of a niche size, numbers of searches, alternative keywords and etc. However as a drill down, I use Market Samurai - for an easy and fast check to find the best keyword to use amongst similar alternatives - in terns of traffic, competition, monetization and much more.
I wholeheartedly agree with the above post. I've always used the simple Google adwords tool and it's hand down done the best job for me...and the price is right too!
Google Adword is best keyword tool. This tool is built-in with number of features and online research analysis. Lots of websites are using Google Adword tool as third party. I always choose this tool to research any keyword for different niche and for articles creation. I get best keyword analysis from this tool and design my strategies according to selected keywords.
Agree that Google's own tool is the best. The numbers are fairly accurate, although not perfect. Consider them ballpark numbers, so don't hang your hat on them. Another good tool would be Google Insights, which will give you some good geo and trending information, as well as additional keyword ideas based on rising searches.
It Depends on your need, If you are searching keywords for SEO then choose keywords manually. If you are looking for your adwords campaign then there is no doubt; adwords keyword tool is perfect as well as if you are using adcenter, their keyword tool will provide best result.