There's really no best boat insurance because most boat insurance is the same in coverage but the main difference is in price of the boat insurance.
Boat insurance will cost you around $500.00 to $800.00 per year depending on the policy and the coverage you get.
If you're a professional fisherman then Markel Boat Insurance is the best as it's been recommended by professional fisherman.
But for just regular boating Allstate is the most affordable and then Progressive is another good boat insurance for safe boaters.
I have my boat insurance through Progressive Insurance and they've been great and pretty affordable.
I pay $500.00 per year for my boat insurance through Progressive as I have it bundled with my homeowners insurance and Auto Insurance.
So if you already have insurance through an insurance company it's usually best to bundle the boat insurance with them for a discount.