Enterprise was the first CVN, Nimitz the first class

Which ship and class came first among nuclear-powered aircraft carriers?

USS Enterprise was the first nuclear-powered aircraft carrier and a single-ship class; the Nimitz class was the first multi-ship CVN class.

The answer separates the first individual nuclear-powered aircraft carrier from the first class of such ships. USS Enterprise stood alone as the sole member of her design. Nimitz therefore began the first recurring class of CVNs, even though Enterprise entered service earlier. The distinction helps readers interpret claims that otherwise use 'first nuclear carrier' and 'first nuclear-carrier class' interchangeably.