Please tell which is the most powerfull tool in the SEO?
I think back links on highly rated websites is the most powerful tool
Well, there are many tools for SEO but I don't use tools for off-page work, I use SEO processor plugin for on-page optimization purposes.
Google adwords and Google trends are most powerful tool in SEO.Because it helps to find the related keywords for website and also full statistic about your related keywords.
Keyword research tool is the most powerful than any other tools. Then analytic and webmaster tools. I highly recommend Google keyword research tools (instant search as well) and word tracker is the best tools.
You can check out backlink checker tool, its one of the most effective tool in SEO.