I know google adwords traffic estimator and semrush. How large difference are there between the estimated data and the real data? Is there others? Your idea will be appreciated.
Every keyword traffic estimator provides different data. I've seen small differences between the data from different keyword tools for some keywords, and large differences for other keyword, differences of thousands of views . I believe the Adwords Keyword Tool is one of the most accurate tools, since it belongs to google, and they have the most accurate data. That's the one that I use.
Most of the keyword tools are very inaccurate. The only way to really tell how many impressions a keyword will get is to do a test campaign.