It depends on the objective of your map.
For navigation is better that you use LWS
(because if anybody in a boat reads in the map i.e 3 meters, the water below has a minimum of 3 meters deep;
otherwise he/she coud read 3 meters, and hit the bottom and sink ´cause there is 1 meter of deep)
On the other side, if you use MSL, please adda a big "Not Intended for navigation"
Regards.
Art