Most stringed instruments have softwood tops, because softwood is light, very stiff and strong for its weight (vibrates well). Alpine spruce is traditional for violins/violas/cellos/stand-up basses mostly because it was the stiffest wood for weight in the world such instruments were invented.
US makers added Engelman spruce, and Sitka spruce. Sitka spruce is sort of the international standard for strength and stiffness to weight. It was used for wooden airplanes, and still is. It's a phenomenal spar wood, but is also getting scarce in the sizes and cuts that make it cost efficient as opposed to materials efficient. Sitka is a benchmark wood, in tonewoods, my impression is that most of it now goes to Asia for making pianos and stringed instruments so they can ship them back to us. Eastern cedar, the kind formerly used in canoes & is white, is also a big tonewood. (NOT juniper, the knotty "red cedar" stuff that is used for chests and to line closets).
In recent years, redwood and sometimes western red cedar have become the chi chi tonewoods for many high end custom guitars. Since an individual beam from a bridge, mine, or tunnel somewhere can sometimes yield hundreds of guitar sets, the really chic redwoods have names like "Lucky Strike" "Tunnel" and i forget the bridge one. etc, etc. "Sinker" redwood used to be hot, but some high end makers sort of disproved it was good for tops compared to redwood that had not been sunk underwater for a few decades. And of course all of those woods can also be had torrefied. Like cues, depends where you think the magic will come from.
New/recent growth redwood generally has widely spaced grain lines because they grow like a weed in more open spaces.
Old growth redwood, like most of us save, has very fine, closely space grain lines because the giants grew in forests where a sapling had to grow straight up to get any light, and then spent centuries competing with the trees around it to add girth through soil nutrients, light, and weather.
This is the kind used for tonewoods. Tops are all quarter sawn, and the best are fine grain, straight up and down vertical grain.
Backs are dense hardwoods, like Brazilian rosewood, Madagascar Rosewood, Ziricote, cocobola, sometimes wenge, ebony or Macassar ebony, etc, etc.
The dense backs reflect and emphasize the vibrations from the stiff tops. Maple and birch have been used. and a range of other cue woods. Some guitars are made with softer, traditional woods like mahogany, for a different tone/sound, etc. I am not a luthier, but the only hardwoods i know of ever being used for tops are sometimes mahogany, and occasionally Koa. It's like cues, in a way - Koa has a better rep for appearance, than it does for hit.
This is why i have trouble cutting up boards for cues - wide, thick, dry, blanks are worth a lot more for tonewoods so long as they are quite close to being quarter sawn. Like cues, people appear to spend a lot for looks, so the backs are not as critical as tops for being dead vertical grain - a little off vertical sometime yields more interest, and in scarcer wood like BRW, even stump wood is used because it is so stunning in appearance and apparently fine or better for tone, as well.
