That brushless motors would be the most effective. With the way they're built they could use more electrical power than blown motors given that they are designed for a larger current supply. Since brushless motors do not have brushes, and so the name, they need lots less maintenance. Which means they are highly efficient since there's no current drop due to brushes. RC Boats with brushless motors will also be much faster and they're much less noisy.
With brushless motors becoming extremely popular blown motors are thought old technology. However they’re continue to be relevant today simply because they do provide benefits that brushless don’t. They are much less pricey than brushless therefore if your with limited funds your fortunate. In case your likely to be making use of your rc boat in rough waters or perhaps a dirtier atmosphere because of their insufficient electronics they are able to handle it better since it's not necessary to concern yourself with things being wet or defaced.