Wood. It is still the preferred medium for building most stringed instruments.
One reason is the sound that different woods produce. Different species of wood vibrate differently, thus producing different sounds.
Another reason is wood is fun to work with. And it smells good [most wood anyway]. So, when one is planning, or yes sanding, it is akin to working in a potpourri.
Wood which is grown at high elevation has different properties than if it were grown at a lower elevation. The same species of wood can be remarkably different if grown where the winters are harsh as compared to warm climes.
One very cool thing about the internet, and thus global connections, is that wood is available to we that build instruments that would not be otherwise available. And that wood is properly harvested, properly dried, properly sawn, and properly cared for, and properly shipped. It is not necessarily cheap, of course, but we can get exactly what we pay for. So given enough time, we can experiment with an almost unlimited variety of sounds and textures and smells.