Personally I’d avoid Costco insurance (at least in Northern California). I don’t know if Coscto uses a single underwriter/insurer but whoever they punt your policy to has the absolute worst servicing Imaginable. Every person I know that has had to suffer Costco insurance hated the process of getting a claim through American Connect or whatever garbage insurance servicer they have.
IMO my State Farm quotes were only slightly more expensive than Costco premiums. But to the point of this thread, all auto premiums seem to have bumped up ~30% in the last year even with the cleanest of driving records and having your car garaged and not living in San Francisco or Oakland.