I looked at both sites listed above and find them fair to mid line. try
www.maptech.com click on the server button near the center of the page. they kinda hide it for some reason. it says "powered by maptech mapserver, entre a town, zip code or corrdinates. after it brings up your area requested you can choose between TOPO, NAUTICAL,AERONAUTICAL or NAV. photo. zoom in and see water depth. I've downloaded corrdinates off this in to my GPS to find holes. depending on your unit it will get you within 10' to 100'
CHECK IT OUT,