I just picked up the 770, recomended here. So far I'm very happy. Problem with cases, unless you get the kind that you can shoot in is you have to take them out. I had my last in a otter box but recently was snapping a pic and a wave/wake got me the wrong camera done.
Think its about the same as the 720, but its good to 33 feet, (I'm not planing on going their) shock proof for a 5 foot drop, crush proof to 220lbs. of pressure and has a manometer that measures air and water pressure to check the altitude and depth of your photos