Every SEO data provider will tell you their index is the biggest and their estimates the most accurate. They can't all be right, and in a sense none of them are — every number in this industry is a model of something unobservable. The practical question isn't "who's right?" but "whose model is strongest for which job, and what does honest access cost?" Here's the 2026 landscape, judged on exactly that.
The majors, one honest paragraph each
Ahrefs — the link-data standard
The crawler and backlink index are the best in the business, and Domain Rating has become the number the industry quotes in pitches, prospecting and hiring posts. Keyword and organic-traffic estimates are strong because they're grounded in that ranking data. The catch is programmatic access: plans start around $129/month (as of August 2026) and the API belongs to higher tiers, so builders pay for a dashboard to read three fields. Best for: anything link-related, SEO-led competitive analysis. Reliability: excellent on links; organic traffic is an estimate and reads low on non-search-driven sites — by design, as we covered in the Ahrefs-vs-Similarweb comparison.
Semrush — the widest suite
The broadest toolbox: keyword database, site audits, rank tracking, advertising research, its proprietary Authority Score. As a daily-driver platform for a marketing team, Pro at $139.95/month (as of August 2026) earns its keep. The API is the sore point — it requires the Business tier at $449.95/month plus metered API units. Best for: teams living in one tool all day, keyword research depth. Reliability: keyword data is top-tier; traffic estimates are serviceable but not the reference.
Similarweb — the traffic reference
For total-visit estimates, engagement and audience mix, Similarweb's panel-plus-clickstream model is the industry reference — strongest on big consumer sites, weakest on small niche domains the panel rarely sees. Seats start at $149/month (as of August 2026); API access is a separate enterprise conversation, typically annual. Best for: audience sizing, market intelligence, sponsorship math. Reliability: the best all-channel estimates available, still estimates.
Moz — the approachable veteran
Moz invented Domain Authority, the metric half the industry still says when it means "authority score". The link index is smaller than Ahrefs', the pace slower than it once was, but pricing is gentler (entry around $49/month as of August 2026) and the API is accessible without enterprise theater. Best for: smaller teams standardized on DA. Reliability: solid but from a smaller index; DA moves a little slower than DR on new sites.
Majestic — the link specialist
Does one thing — link data — with its own useful lens: Trust Flow vs Citation Flow separates "many links" from "good links" in a way single scores blur. Around $49.99/month (as of August 2026) with API access at reasonable tiers, it's the quiet workhorse of link auditors. Best for: deep link forensics, cheap link-data API. Reliability: excellent within its niche; no traffic or keyword story at all.
Google's own free sources — ground truth, for your sites only
Search Console is not an estimate — it's Google telling you your actual clicks, impressions and positions. Trends adds relative demand curves. Free, authoritative, and structurally incomplete: no competitor data, ever. Best for: everything about your own properties. Reliability: the only "measured" column in this article.
The comparison table
| Provider | Signature metric | Data strength | API entry reality | Entry price* |
|---|---|---|---|---|
| Ahrefs | Domain Rating | Links, organic estimates | Higher tiers / enterprise | from $129/mo |
| Semrush | Authority Score | Keywords, breadth | Business tier + units | $139.95/mo ($449.95 for API) |
| Similarweb | Total visits | All-channel traffic | Separate enterprise contract | from $149/mo |
| Moz | Domain Authority | Links (smaller index) | Accessible | ~$49/mo |
| Majestic | Trust / Citation Flow | Links (specialist) | Accessible | ~$49.99/mo |
| Google (GSC/Trends) | Clicks (measured) | Your sites only | Free API | $0 |
*Published entry list prices as of August 2026; every vendor changes these at will — check their sites before budgeting.
How to judge "reliable" in this market
- Estimate vs measurement. Only your own analytics and Search Console measure. Everything else models. A provider that admits this in its docs is more trustworthy than one that doesn't.
- Index size vs freshness. A huge link index crawled slowly misses the links you earned last month — the ones you're trying to evaluate. Ask when, not just how much.
- Panel coverage vs your niche. Traffic panels are strong on mainstream consumer sites and thin on niche B2B. The smaller the site, the wider the error bars.
- Provenance. Can you tell, per number, where it came from and when it was fetched? If a tool blends sources silently, you can't debug a weird number — and weird numbers are half of this job.
The two-provider answer
For most builders and agencies, the practical conclusion isn't picking a winner — it's cross-checking two independent models: one link/organic view (Ahrefs-grade) and one all-channel view (Similarweb-grade). When both agree on direction, act with confidence; when they diverge, that divergence is itself the finding.
Full disclosure of where we sit in this landscape: SEO Metrics API isn't another index — we're an aggregation layer over it. One key returns Domain Rating and organic estimates fetched from the Ahrefs API alongside Similarweb-style visit estimates, each field stamped with its provider and fetch date, from $0. If the two-provider answer is the right one for you, that's the cheap way to get it — and the docs show exactly what comes back before you sign up for anything.