I highly recommend you to use Semrush for better keyword research. It is one of the best tool to find high performing keywords. Alternatively you can also use Longtailpro as well.
Did you mean keyword researching tool? If that right then Google Keyword Tool is the best free one and SEMRush or Longtail is the best paid one. IMO
Hi Jack, If you want to do niche keyword research, go with Keyword Revealer. You can try it FREE but it's a premium tool. Moreover, SEORUSH is also a great tool for competitors keywords analysis and finding optimum keywords. Ahrefs is one of the pretty tools. For free Google Adwords is also good for finding group keywords. To extract Google suggestion based keywords, try ubersugegst (That's FREE). Hope you get your answer!