Can't go wrong with the Google Keyword tool, SEMRush and Google Trends. The Keyword tool for volume estimates, SEMRush to see what keywords competitors are ranking for/targeting, and Google Trends to make sure the traffic is actually coming from countries I'm trying to target. Gives a relatively accurate picture of when to expect traffic spikes and seasonality insight.
Unlike similar tools, Serpstat is a page-oriented platform for in-depth competitive analysis. You can find competitors and define missing keywords for a single URL or even entire domains. You can also view historical position data for a range of pages organized by phrase, as well as see which pages have dropped in rank and their rank distribution as a percentage, which is very handy if you want to compare data from two different time periods or observe changes over time based on algorithm updates and other factors.
1) SEMrush - I believe that among all the 3rd party software, SEMrush has the largest keyword database. Their search volume data is pretty accurate and aligns with the Google keyword planner. Also, based on the type of content that needs to be produced (i.e. informational, transactional, etc.), one can utilize different filtering options available in it.
For a long time, I wanted to develop a tool for content marketers that would assist in the process of coming up with blog ideas and subjects. Upon researching developers for this concept I had, I stumbled across Long Tail Pro, and realized instead of developing a tool myself for fellow bloggers and content marketers, I would throw my support behind this one.
We’re not here to dwell on the good and the bad of Google’s decision. I personally am elated that this debate has brought the crucial SEO function of Keyword Research into the limelight once again. There’s more to it than taking the first 10 results from the Google Keyword Tool and scattering them left, right and center in your content. Savvy keyword research is what separates strategists from headless chickens.
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input. In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).