Ahrefs, Semrush, and Ubersuggest all use their own keyword difficulty (KD) formulas, so “better” depends on your SEO goals:
Ahrefs calculates KD almost entirely on backlink profiles of the top 10 ranking pages. This makes it more accurate if your focus is link-building, but it may underestimate difficulty for keywords where on-page factors and topical authority matter more.
Semrush uses a mix of backlinks, SERP features, authority score, and traffic trends, making it broader in scope but sometimes overestimating difficulty for long-tail keywords.
Ubersuggest takes a simpler approach, smaller backlink data and more emphasis on on-page metrics, so its KD scores can be less precise but still useful for beginners or low-budget projects.
Tip: If you’re doing local SEO, none of these tools’ KD scores perfectly reflect real competition because they usually calculate difficulty at a national/global level. For the most accurate picture, combine KD scores with manual SERP checks, local pack results, and competitor audits.