Ahrefs, at $29/mo against $139/mo.
Ahrefs vs Semrush
Ahrefs is cheaper at $29/mo, against $139/mo.
Keyword research and backlink analysis

All-in-one SEO, content, and competitor tracking
Ahrefs and Semrush are alternatives in the SEO category. Ahrefs: Keyword research and backlink analysis. Semrush: All-in-one SEO, content, and competitor tracking. Ahrefs is cheaper at $29/mo against $139/mo.
Keyword research and backlink analysis. It sits in the seo category, and ships in 1 tested stack here.
All-in-one SEO, content, and competitor tracking. It sits in the seo category.
They are alternatives at the same step, so most stacks pick one or the other. No aistack.sh stack uses both today, though nothing prevents a custom workflow.
Beyond each other, Ahrefs's closest alternatives are tracked in its tool page. Semrush's closest alternatives are tracked in its tool page.