National Corvette Museum Insurance has been and still is my choice and have referred many dozens of folks to them over the years and have only heard positive, some VERY positive feedback from them.
The BIG Plus are the people that you deal with. They KNOW cars and are efficient, competent and downright NICE! Every one of them!!!
American Modern as others have said offers great product at a very competitive price.
However should the SH** hit the fan the agent is as important as the insurer, and that is where NCM is exemplary.
I have used most all of them over the last 35 years, but NCM is it for me!
While your mileage may vary, those are my experiences.
Marty