The main thing that makes Valyrian steel better is that it’s lighter, stronger, and sharper than ordinary steel. So it’s going to be better with weapons that take advantage of those properties:
- Axes: the sharper part will certainly help the axe improve its ability to cut into things, and the stronger part will prevent the axe-head from breaking but that’s pretty rare. The lightness thing doesn’t help – axes want weight behind them so that all that momentum gets channeled by the wedge of the blade to a point.
- Hammers: Same thing that goes for axes wrt to lightness goes doubly for hammers. The less a hammer weighs, the less impact it has. However, the sharper part will help with the pick end of the warhammer. Overall, not really a good idea.
- Spear: Think of a spear as a sword blade on a stick and you begin to see why a Valyrian spearhead would be very handy – lighter spears make it easier to fight longer or to throw the spear, sharper spears make it easier to puncture shields and armor, harder spears won’t break or bend when they hit something. Now, as with the axe, there is an issue that doesn’t crop up with swords: spears and axes are on wooden hafts, which can break or be cut through and then you’re screwed. However, if you have enough metal for a Valyrian steel shaft, then you’ve got something really special.
- Halberd: as discussed before, a halberd is basically a Swiss army knife of polearms – it’s an axe, a spear, and a hook. Valyrian steel aids in 2/3 of those, so it’s not a terrible idea. However, it also has the same haft issue but more so because it’s a polearm and has a longer haft.