[HoneyBadger]

Spears are better, because they extend reach, and because they only require a tiny space to thrust forward, which means they can fit into narrow confines, and can be weilded by more combatants, against more opponents, in a given area-thus, the phalanx. And phalanxi are the way to go, underground, where there isn't a lot of maneuvaring possible, or necessary, and where you can usually guess where your opponent is going to come from.

Shortswords are good for dwarfs for the same reason they were good for the Romans-they don't require a lot of room to thrust, preferrably upward under armour.

Machetis are good for three reasons-1: they're versatile, 2: they're tough weapons that can take a lot of abuse, and 3: they're good for clearing underbrush, and when you're a dwarf, not used to being on the surface and having to deal with underbrush, you want to be able to hack through it so you can see, and move.