I'd have to go with driving being more dangerous by far, not sure when everything is relative but as long as you stay out of pirate waters and beware of hurricanes, you should be alright as long as you have a good boat and know how to sail. Powerboats on the other hand, things may be different, but I'd say cars by far still. That's why I'd opt for #vanlife... more risky = more fun in most cases. Sailing I can see being fun for a week or so then I'd say... screw this. That's subjective though.
I am going to "guess" driving is more dangerous than sailing, especially considering that most accidents occur within 25 miles of home.
Getting an small RV, actually. It's gonna be me and my dog for 3 months, really looking forward to it! So far I decided to go with the solution suggested by Kevin, just feels like it's the right kind of setup.