The Wood Database presents the hardest woods.
8. Black Ironwood
7. African Blackwood
2. Lignum Vitae
You'll have to click through to find out what number 1 is! All perfect names for weaponry materials in a wood-themed RPG. And here's the softest woods, which is only lightly spoiled by pointing out that "nothing else comes close" to Balsa except Quipo, which is of similar softness to Balsa and "virtually unobtainable".