The best boat loan is cash. I know, I know. Who can do that? Not me. But it is the best. Seriously, the personal, boating value of our Cdory went way up the day we paid it off. We took out a very short loan, 5 years, and it hurt every time we made that big payment. But, 5 years have gone by quickly and boy do we enjoy being on the water better now that we are boat owners, and not "renting" the boat from the bank.
I'd shop for the shortest term lowest interest you can possibly afford. In our case, it was the CREDIT UNION. The 10 and 12 year loans look real nice relative to buying a more expensive and bigger boat, but that's a lot of great boating money that is going to interest and a painfully long time to pay for a luxury.