I'd take the car if there wasn't a large sum of money included. I've owned boats most of my life and believe me they cost a lot of money to keep in a slip and maintain each year. Even a "normal" boat will cost you $5k - $10k a year to maintain. A car you just need a secure covered place to keep it.
Slips for luxury boats can run several thousand dollars a month to rent. Add in 10% of the price of the boat per year to just keep it floating and in working order.