Well, first of all you need to post it in both. That will bring you the most exposure. At the same time, it depends on what you are selling and how people will come across your boat. If it's a custom boat, people will most likely come across that boat while searching for that particular model.
I found out in selling my Monterey 206 Bowrider some two years that comparable boats(remember it's a bowrider, now a custom boat) were selling for much higher in the magazine than online. People who purchased the magazine had a lot less other bowriders to compare it with so I got the most out of the buyer.
I found that boat on-line for $10,000 and sold it in the mag for $12,000 two years later and it was the same exact boat with a wax job.