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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 hookbill is pretty nice. Plenty of options, pushing/pulling, blunt or edged attacks. A mace is reliable and easy to use for survivors that may be gun shy.