Well, some are worse than others, but not all insurance companies do business in all states.
Most states, on the state insurance department website, will publicize the upheld complaints - so you can flat out see, by line of business, which insurance companies have "done wrong" by their customers and had their hands slapped by the insurance commissioner - name, and number of upheld complaints.
Most companies are about the same. You can go to the insurance department website and look under complaints to see which ones may have the most problems.
But as a general rule, you will see more problems with 'HIGH RISK" insurance companies. Not because they are bad, but because they insure some of the worst drivers out there, since other companies wont touch them; ie; DUI, tickets, multiple accidents, lapsed policies.
With high risk companies, many of the people refuse to cooperate with their insurance company. The company may deny the claim due to no coverage; ie; policy lapse, driver or vehicle not insured with the company.
It depends if you have had an accident and if you settled with a insurance company if afterwards you felt you were treated fairly or not.
Not Geico! I have had 3 claims with them and they were incredible! Usually those discount ones are pretty bad. I worked for a rental car company that did mostly insurance rentals and the discount ones treated the customers terribly. Late payments, refusing to extend rental days while their car was still being worked on, Not covering collision if the person only had liability. You should ask the people you trust who they use and if they have had any experiential stories that could help you. Geico has been incredible for me and my spouse. Make sure you tell them if you belong to any clubs or graduated because they give little discounts for it. Hope this helps!
The real answer is all of them, or are you looking for the worst of the worst?