A good question to ask a prospective Insurer is to ask the question "who underwrites your policy"? Rarely will it be the company you are purchasing the insurance from. That's not necessarily bad, but some of the next questions to ask are "who are your adjusters"? "Do your adjusters specialize in Classics" "Do they work for your company or the company underwriting the policy?" "What is your policy on repair?" "Are you willing to repair my car the correct way and restore it to 100% pre accident condition, using the same methods as my car was constructed? "What about repair Shops" Do you have a network of qualified shops or shops that you recommend?"
Lot more to it than just the lowest price IMO. What if your car was metal finished. You get a dent in the door. "Is your Company willing to pay for my door to be finished the same way as it was originally?" Most of the time they will not be. So now you have a door with filler in it.
One particular example I have experience with was a 1940 Ford that was painted candy apple red. True candy color, gold base, red candy mid. Front end hit. Damage to the fenders, grille, and hood. Adjuster had no knowledge of candy paint and would only write it to blend. Blending candy is essentially impossible. We tried to tell him that. Went around and around for several weeks. Adjuster would not write it for a complete repaint. Customer got tired of waitng and ended up paying the extra cost to have the car redone completely. Idiot adjuster never did admit that you can't blend a candy. Customer had "classic" insurance through State Farm.