Research depth
Discovery
How well the tool supports keyword, competitor, SERP, backlink, or market research before execution.
cognitiveSEO
Broad first-party SEO research coverage across links, rankings, keywords, competitors and site issues.
The homepage lists Site Explorer, Keyword Tool, competitor strategy research, backlink analysis, rank tracking and a comprehensive Site Audit: https://cognitiveseo.com/
Serpstat
Very deep SEO research coverage across keywords, domains, competitors, backlinks, PPC, and SERPs.
Features lists keyword research, competitor/PPC analysis, backlinks, batch analysis, clustering, and keyword trends; https://serpstat.com/features/