Google keyword planner is the best free tool for high quality keyword research. They help to provide various keyword suggestions for your domain, and selecting the right keywords will help to rank your website higher in search results.
As an all-in-one SEO/PPC platform we take regular checkups and comparisons of keyword databses among the most prominent players like Semrush and Ahrefs. From the keyword research perspective, it's realy hard to pick just one tool and stick with it.
Keyword planner,KeywordTool.io,Ubersuggest.org, Keyword Discovery if you want to know about these tools i detail you can refer to Checklist for your Keyword Research blog.