In regards to your opening thread, in adverse to giving and providing you the best tool, which can be an opinionated or chosen by personal preference, I will provide a reputable link via MOZ that offers their thought process on
Best Free SEO Tools & Resources. Be aware it's a blog article from 5 years ago but does provide a variety of tools and then from such info you can make your own decision on what might work well for.
The 100 Best Free SEO Tools & Resources for Every Challenge
https://moz.com/blog/100-free-seo-tools
I would also suggest to browse these forums to find other similar threads on the same topic.