Which of the following organizations is known for rating insurance companies?

A.M. Best Company is recognized as a leading provider of ratings and information on the insurance industry. It evaluates the financial strength and creditworthiness of insurance companies, helping consumers and businesses assess the reliability and stability of insurers. A.M. Best's ratings are particularly important for policyholders and investors as they indicate how well an insurer can meet its ongoing insurance obligations.

In contrast, the other organizations listed, such as Goldman Sachs, J.P. Morgan, and Fidelity Investments, are primarily focused on investment banking, financial services, and asset management, rather than specifically rating insurance companies. Their operations do not involve the comprehensive evaluation of insurance company performance or solvency that A.M. Best specializes in. Thus, the correct answer is A.M. Best Company, as it is directly associated with the evaluation of insurance companies.