No matter how low the premium or how much the policy promises, if your insurer goes out of business, youre sunk. Short of that, you want a firm that will handle your claims promptly, courteously and fairly.
Many insurers have been around a while, and arent likely to disappear any time soon. Several independent companies provide detailed ratings for insurers financial soundness, including A.M.Best, Moodys, Duff & Phelps and Standard & Poors, if youre concerned about an insurers viability.

Customer service, please

For most people, customer service is the more pressing concern. You dont want a company that routinely turns your claim into a years-long siege. Ask friends, families and co-workers to recommend an insurer, and see how their candidates compare.
You can also check records of formal complaints made against insurers state-by-state. The National Association of Insurance Commissioners keeps track.

Ready for some money-saving ideas?

Cost, coverage and reliability - these are the main factors.
Review all three every year or so to make sure youre not paying too much for car insurance.  Look at the numbers. Test them yourself on the calculators to find the very best insurance deal for youre the specific life you happen to be living right now.
After all, insurance really ought to set your mind at ease.