The best wood isn't quite wood! A speaker cabinet needs to be as non-resonant as possible. Generally, that means either dense plywood (birch ply is good) or MDF fiberboard. 3/4" thickness is standard. 1" if you're a perfectionist (and aren't worried about a hernia!). Internal bracing is often a good idea too. Actual wood will resonate and add sonic coloration to the sound in unpredictable and usually undesirable ways.
For appearance, a hardwood veneer is usually applied. Or you can use thinner MDF/ply substrate with a thicker hardwood overlay; for instance, half-inch MDF glued with quarter inch hardwood facing. You can also use laminates or paint to good effect. Skillfully applied lacquers or automotive finishes can look great!
Some DIYers and high-end mfrs use Corian. Overly heavy, overly expensive and generally overkill, IMO, but if you have the budget and fabrication skills and like that look...