I was with BoatUS for years, but after Sandy my premium almost doubled - I live on a lake in NC and have never had a claim. When BoatUS could not give me an explanation for the increase other than "Sandy" I decided to shop around - switched to Progressive. Never an issue with BoatUS or Progressive (have had the boat and SeaDoo with them for 4yrs). But then again, never a claim to deal with either.
NBOA, had my 290 SeaRay with them when I first bought it, got the first renewal and had a question, after 3 days I finally got someone on the phone - figured if it takes that long to respond when there IS NOT a problem, can only imagine when there IS a problem, dropped them right then.
StateFarm - have had my home and cars with them for years, every couple of years I have my agent quote the boat and SeaDoo, premium is always ridiculously high. Even my agent agrees I should stick with other carriers.
Unfortunately you never know if your insurance is good until you have a claim - then it's too late to switch.