When I went to insure my dads 1998 c200 I found 1st central to be cheapest by far and almost half the price of everyone else. Tried classic specialists including Adrian Flux and they were around the same as everyone else for me (31 year old with another car and 2 years no claims available for that car and 6 years on my main car).
I just used the comparison sites and tweaked things like mileage (only 3000 a year) until I got it as cheap as possible. Asking for a recommendation is a bit pointless really as everyones quotes will be different.