There are five widely used systems. It has a rating system that includes fifteen categories. One rule of thumb suggested by the Insurance Forum, an widely followed newsletter, is to insist on high ratings from at least two of the four rating services which it follows. It has various definitions of high ratings that vary from one service to another. Ask the company or agent for the financial rating of the insurer and what it means.
Many libraries have books or other publications with ratings of insurers.
Don't drop an existing policy in order to buy a new one, without talking to the company and agent that wrote the policy, and without getting proof, in writing, that it is advantageous to do so. There are many reasons why you have to be cautious in replacing policies, so don't move ahead on a policy replacement unless you are sure you know what you are doing. One of the major ripoffs of the life insurance industry is getting people to drop old insurance to get at its cash value in order to buy a new policy. Given this incentive, the stage is set for replacements that enrich the agent and defraud the policyholder. Some replacements make sense, but don't go for one that you don't understand.