A good notebook bag should offer both impact protection to protect it if it falls from a height, and crush protection - when a heavy object is placed on top of your notebook carrier. Most conventional laptop carriers offer a soft-shell external system combined with several layers of soft padding or hardboard. But this is not the best shock protection for your laptop. An external hardshell system made of monocoque ABS, moulded plastic fibre or aluminium will offer great crush protection, but unless there is a good layer of soft-material such as foam padding between your laptop and the external hardshell system, your notebook could still suffer from impact damage. There's more than one way to carry a laptop bag, though most laptop bags come with the basic shoulder sling and a standard handle.
Laptop bags are now also available in the form of haversacks, with dual shoulder straps.
Some laptop carrier vendors have even modified light-duty dispatch carrier bags to carry laptops. These bags, made popular by the Australian surfing fashion shops, are a practical and attractive way to lug your laptop around. Shoulder sling systems are an easier way, but may cause unwanted shoulder ailments over long periods. Make sure your shoulder sling is well-padded and that it distributes the weight of the notebook compartment properly. A dual sling notebook haversack is the best way to carry a heavy laptop because it distributes the load between your back and your shoulders.