I’m a bit torn between a splitting axe and a mace/morning star of some sort.
An axe offers better penetration and is useful for other tasks aswell but perhaps posseses greater risk of getting stuck. A mace is not as versatile but is highly effecive when making direct contact with the skull and is unlikely to get stuck. A mace is also easier to improvise and customize for individual preferences.
A kukri sounds like a good example of what you are suggesting. It’s an Indian dagger/short sword that has a recurve and a thicker portion from the middle to near the end of the blade moving the center of gravity up and adding a heft that gives the weapon an effective chopping ability. In addition to being a weapon it is effective as a utility knife and as a light axe.
https://en.m.wikipedia.org/wiki/Kukri