The siding on a shed will potentially take more abuse than siding on a house -- the first couple of feet of the side of the house is usually concrete foundation, but the shed goes right down close to the ground, and gets hit upon by bicycles, shovels, lawnmowers and everything else that moves in the back yard.
The most damage resistant siding is fibre-cement siding, followed by real wood siding. For both, dents and scratches can be easily re-stained. Aluminum siding will dent very easily and always look banged up. Vinyl siding resists scratches and even dents pretty well, but in extremely cold temperature, it will actually crack rather than dent.