The first three SEO tools that I have ever tried would be SEMRUSH, Google Keyword Planner and Scoop.It. As Google Keyword Planner was free, I tried it first. It helped in optimizing my contents a lot and it also produces great unique keywords too. After this, I used SEMRUSH and Scoop.It. I used their free version and paid version, both. Currently, I am using SEMRUSH but I like shifting from one SEO tool to another. But if you want me to select a winner, it would be SEMrush.