What companies provide authoritative rating guides for the nation's insurance companies?

AM Best is perhaps the most well known institution that has been rating insurance companies for over 100 years. Also in the same way there are Standard & Poor's and Fitch Ratings that do provide ratting services for insurance carriers based on their financial strength. JDPower is another institution that ranks several other organizations including insurance companies. This institution however does not rank the vast majority of insurance companies, especially local, small size insurers. One of the respected aspects that JD Powers rate insurers is by their "auto insurance claim rating."