I've had most of my cars through Tower until the BMW, they wouldn't insure my Fiancee' as she's under 25. Not even at a higher rate, just out right wouldn't.
So I have the BMW through State. Previously had my RS Legacy Rally car through Ando I think it was. That was my most difficult car to insure for sure. Otherwise had a few through Classic Cover, and NAC.
I've never had to make a claim with any of them, so don't have any experience there.