Paychex sits in the same bracket as ADP and competes on service. The pitch is a named payroll specialist who knows your account, and for businesses that have spent an afternoon in a support queue, that is the whole argument.
What it does well
The dedicated specialist model is real, and the reviews that praise Paychex almost always name a person. Onboarding and migration are handled rather than self service, which matters if you are moving mid year with filings already in flight.
The HR side is strong. On higher tiers you get handbook building, compliance support and an HR professional, which is enough for a business under about 100 people to not hire an HR generalist yet.
Tax and filing
Full US coverage: Form 941, 940, W-2, 1099-NEC, plus state and local filings, all filed and paid on your behalf. New hire reporting is automatic.
Canadian payroll exists under a separate Paychex agreement covering T4, ROE, CPP and EI. As with ADP, one vendor, two contracts.
Where it frustrates people
Pricing is quoted and add on heavy, and the reviews consistently mention fees appearing that were not in the original quote. Service quality tracks the specialist you are assigned, so experience varies more than it should. The interface is functional rather than pleasant, and the mobile app lags the web product.