Most important electronic equipment
It also depends a bit on what you''re sailing/motoring. On our catamaran we typically see danger before we hit it - as we only draw 3 feet. Even in Maine, the water color changes significantly as the depth changes from near surface (i.e. less than 3 feet) to greater depths. My issue with our depth sounder is that it does not look ahead - i.e. you don''t see rapidly rising rocks in time. Someday I may go for a forward-looking/scanning variety to give protection to both hulls and better warning.
That being said, I still prefer a working DGPS over a depth sounder for the parts of the world we currently sail in. On our boat, a lead line gives the same result as our depth sounder, does not rely on electricity, etc. Approaching any anchorage at night or in foggy conditions is risky and if you don''t know your way around it''s better to stand off until conditions clear. Sailing is not about keeping a schedule but getting there and back in one piece.
But my choices would change if I were sailing around the world. There, a forward-looking, scanning depth sounder might be a requirement given when some of the surveys were made that make up our maps, the positional errors, etc. I thought most of the rough positional errors were supposed to be addressed via space-based surveying but I guess this has not yet happened...
Anyway, the original question referred to what one would want to integrate. I prefer radar to date b/c such overlays allow you to easily differentiate fixed objects such as buoys and land masses from other objects like other ships. My next radar, GPS chartplotter will have such functionality (5+years from now).