I dont know what the other islands are like, havent dove them. Oahu is home for me and i love diving here. Never got to dive in March, but I heard stories from everyone, whale this, shark that. Just yesterday we were 100 yards from some whales. We heard them loud and clear and went looking for them, but they were in a sandy patch we didnt go too. We saw them when we got on the surface. Hawaii is great year round, and late March sharks cove MIGHT be opening up for cheap shore dives that are fantastic. Hope you find what your looking for.