You can decide which is the right material for your kitchen by looking at the style and the accessories that you already have. For cottages and smaller kitchens, wood is a popular material. There are many wooden salt and pepper mills, for example, the Chess pieces.
Glass is another common material to use in the manufacturing of salt and pepper mills. You can easily see through the glass to monitor how much salt and pepper remains, and top it up as necessary.
If neither wood nor glass is suitable for you, consider ceramic. A popular material which can be hand painted easily to suit your tastes, it is versatile and flexible to suit many surroundings.