Almost every SEO project starts inside one of these suites: finding keywords, sizing up competitors, checking a backlink profile and auditing the site. They overlap heavily, so the real decision is which one has the best data for your market and which interface you will actually use every day. Below is what each is genuinely best at, and where it falls short.
The tools
Ahrefs
Ahrefs started as a backlink tool and still runs one of the largest and freshest link indexes on the market, which makes it the default choice for link analysis and competitor research. It has since grown into a full suite covering keyword research, rank tracking, site audits and content exploration, so a solo consultant or small team can run almost everything inside it. Its traffic estimates and keyword-difficulty scores are widely trusted as directional signals, as long as you remember they are models rather than Google's own numbers. If you only buy one all-in-one platform, Ahrefs is the safest default.
Semrush
Semrush is the broadest of the suites, stretching beyond SEO into paid search, social and content marketing, which makes it popular with agencies that want one tool across channels. For SEO specifically it is strong on keyword research, competitor gap analysis, rank tracking and site audits, with an especially deep keyword database. The trade-off for that breadth is a busier interface and a higher price once you add users and projects. Choose it when you need one platform to cover more than organic search.
Moz
Moz is the lighter, more approachable option, best known for popularising Domain Authority (DA) as a quick proxy for a site's strength. It covers the essentials — keyword research, link analysis, rank tracking and audits — in a cleaner, less overwhelming interface than Ahrefs or Semrush. Its link and keyword data is smaller and less current than the two market leaders, so it suits smaller sites and people learning SEO more than heavy competitive research. Treat DA as a rough comparative signal, never as a metric Google actually uses.
Majestic
Majestic is a specialist rather than a suite: it does one thing, backlink analysis, and does it deeply, with one of the largest historical link maps on the web. Its signature Trust Flow and Citation Flow metrics separate how authoritative a link profile is from how large it is, which is useful for spotting spammy or inflated profiles. It has no real keyword or audit tooling, so it is a complement to an all-in-one suite, not a replacement. Reach for it when link quality is the specific question you need answered.
How to choose
For most people Ahrefs or Semrush covers 90% of the work — Ahrefs if links and clean data matter most, Semrush if you want reach across channels. Moz is a lighter, cheaper entry point for smaller sites, and Majestic is a specialist you add only when deep link analysis is the job. Pick one main suite and learn it properly rather than paying for three you half-use.