Unlike a wine decanter, a scotch decanter is not used to help filter out sediments in the drink, since scotch generally does not have any sediment in it. The purpose of a scotch decanter is instead almost purely aesthetic, and choosing a good decanter for your scotch is a matter of finding one that will seal tightly and meet your aesthetic needs. These decanters come in a variety of shapes and sizes, as well as materials, so the first step is finding one that has the capacity you are looking for. From there, be sure to examine the stopper for a tight seal that will protect the scotch from oxygen.
More expensive scotch decanter models may be made from crystal. Such a decanter is often very aesthetically pleasing and highly ornate, and the price will match the materials and craftsmanship. Some such decanters also come with crystal serving glasses to complete the set. This is a good choice for someone looking for an attractive scotch decanter in a formal setting, but care will need to be taken to prevent damage to this expensive unit. Some crystal also contains low to moderate levels of lead, which can leach into the scotch if it is left inside the vessel for too long.
Glass decanters are generally less expensive but often just as attractive. These scotch decanter models are made from the same material as the original scotch bottle, so you will probably want to choose one that is more ornate to justify having a decanter in the first place. The most important feature of any decanter, glass or crystal, is the stopper, which will help prevent oxygen from contacting the scotch, thereby affecting the flavor of the scotch. The color of the glass will have little or no effect on the scotch itself, though darker decanters may be helpful in preventing the flavor from being altered when exposed to sunlight. Exposure to sunlight should be avoided in general, as UV rays can affect the flavor of the scotch.
The stopper itself may feature a cork much like the original bottle of scotch did, or the stopper may be made from glass or crystal entirely. Cork is a good choice because it will expand when stopping the mouth of the scotch decanter, but it will not be the most durable option, as the cork can break down after time. A glass or crystal stopper will need to be fashioned so it fits snugly in the mouth of the decanter to prevent oxygen from entering.