The big difference between the h2oc and the Expedition C, the expedition adds a barometer, altimeter and a magnetic north compass. Meaning if you lose satellites you will still atleast know what direction you are heading with the compass. A nice feature when you are hunting under a heavy tree canopy. Lowrance units will except the standard Lakemaster and Navionics chips.
Garmin units have some nice topo software available for them, good for hunting. The lake maps you need to use Garmins version of the Lakemaster. Same info has the standard Lakemaster chip, Garmin just doesn’t update the chips has often. You will not be able to use Navionics chips.
Difference in the chips:
Lakemaster: gives you all the streets and back roads for the state. It has some really nice HD maps for the popular lakes. And it automaticly loads.
Navionics North: has more lakes per state then Lakemaster and again offers some really nice HD maps. And you get 6 states, ND,SD,MN,IA,WI,MI. The down fall here is the unit is not capable of reading the whole chip at one time, you have to go into some simple menus to load the area you want (not a huge deal). Such as NW MN, SW MN.
The best way to decide what chip will work best for you is to go in to a store have them put the chips into separate units so you can compare the chips side by side on the lakes you fish.
I think most of us choose the lowrance because of the ability to run either chip. And alot of us use Lowrance GPS/finder combos on our boats. The menus are the same and we can easily transfer the way points form our boat unit to our handheld and back.
Alot to think about!
Hope this helps!
Ryno