KW research is much more than just listing some keywords like KWP does. This is why KWP is good for quick lookups but is purely useless from a pro research standpoint.
There is no one single tool. The keyword research process implies multiple tools necessarily.
Just for lookups I like KWfinder, but most tools like Wordtracker, SEMrush, Ahrefs, Keywordtool, and even KWP will do the trick.
If you are looking for ideas, you need a bulk checker with fast autocomplete suggestions. A tool like keyword shitter will massively help you and then you can browse fast and furious with Keywords Everywhere chrome extension to nail down a couple of interesting keywords for your purposes.
Also you could just research by copying your competition. This can be done with any tool that also contains keyword database, like Semrush (the best here), Ahrefs or KWfinder (through Linkminer) (or even Serp Stat)
So personally I constantly use Semrush, Ahrefs, KWfinder and Keywords Everywhere chrome extension on a regular basis.
But you can do all just with Ahrefs and still get similar results. So definitely Ahrefs as the AIO tool is the best.