Polycarbonate cases with scratch the device on its own with normal use unless it has good padding of some sort to separate it from contacting the actual device.
I personaly would get a tick silicone over polycarbonate.
There's also the middle material which is better: TPU rubber. It's softer than polycarbonate so it has some bounce to it, but stiffer than silicone. So the fit and protection is better, IMO.
Hard Candy makes the Sleek and Street Skin cases out of it. Just this morning my Sleek skin protected my iPad from cartwheels all the way down eight wooden stairs onto a wooden floor.
If the silicone is thick, they will provide better protector than the hard case, but we also recommend TPU cases. They are a hybrid of Silicone and Hard cases.
Protection is vague at best. Different angles of impact can mean a major difference in damage potential. The only real protection is a large shell that absorbs the damage. It destructs to save the contents. Look at a race car accident. You have parts flying all over creation, but they do so in a way to dissapate the energy of the crash and save the core.
If the silicone is thick, they will provide better protector than the hard case, but we also recommend TPU cases. They are a hybrid of Silicone and Hard cases.