Let your language and team decide. REST Assured is the mature choice for Java and Kotlin teams that want API tests inside JUnit or TestNG and the same Maven or Gradle build. Playwright's built-in request client suits JavaScript and TypeScript teams, or anyone who wants UI and API tests in one runner, because you can log in through the API and share that state with browser tests. Postman with its Newman command-line runner is best for exploration, sharing collections and involving non-developers, though code-owned regression suites are easier to review in git. Whichever you choose, keep the tests in version control and run them in CI.

Sources: REST Assured, Playwright API testing, Postman: Newman, QASkills comparison