
lemeres |

Mace? Maybe call yourself (or at least the weapon that serves as a badge of office) 'Skull Crackers" or something along those lines.
Anyway, general point- a lot of undead are skeleton based. Not just 'x turned into a skeleton', but things like a mass of skeletons put together, and other various things. Skeleton based undead tend to need bludgeoning.
You could also try making it a paired thing- slashing tends be used for zombies, and swords or daggers are commonly used in normal fights.
So you could make a dagger and mace on your belt into a 'katana and wakizashi' type deal, where you are always sure that you have the tools you need. Maybe not as main weapons- but owning a pair as a badge saying 'I am ready for this'.
Another advantage of mace and dagger is that they are both simple, so everyone can use them to some extent.

lemeres |

I think we can all agree- you want one of the smashy simple weapons, at least as a side arm.
Heck, maybe have a mix of them if the undead slaying group tends towards 'rag tag'. This allows for a variety of people with different styles and aesthetics.
Battle aspergillums are light maxes that can do something with holy water. Nice side arm in general, and great for finesse types.
I like heavy maces, since they can rest better on the hip in a holster. Good for str types since they can be two handed.
Morning stars have piercing (not sure how often that comes up other than one really weird form of zombie). They are spiky, so they can't holster well- which tells people 'I came here to smash heads, not to hang out'. Also, some art for monsters indicates that they can be at the level of 'baseball bat with nails stuck in it', if you want someone really rough and tumble.
But make sure that someone always has something smashy. That can be the shared sign that 'we are ready for this. We know what we are doing'.

pocsaclypse |

Bashing and slashing weapons will take you the farthest against undead. Almost none of them have dr piercing last time I checked and 3 of the 4 that did were dr/piercing and wood so go ahead and keep a stake around just in case.
Maces and battle aspergillums are going to be solid choices for bashing weapons since im pretty sure everyone can use them.
For slashing weapons, you will rarely go wrong with a good old fashioned long sword but if you arent proficient then I think daggers are the only simple weapons that do slashing.
Silver is far and away the most common material for overcoming undead dr with only a few (like 5 tops) that need cold iron, adamantine, or wood.
At higher levels youll start seeing dr vs magic and good as well.
So it turns out the best undead slayer is a dwarf with a healthy selection of maulaxes

lemeres |

For slashing weapons, you will rarely go wrong with a good old fashioned long sword but if you arent proficient then I think daggers are the only simple weapons that do slashing.
There are a few, but they can be summed up as 'worse than daggers'. Nothing that can be properly two handed.
I am pretty sure that this is a weird balancing thing that was grandfathered from D&D. There are a ton of piercing weapons in simple weapons, but no slashing weapons that can be two handed. This might be because simple weapons are supposed to be 'worse' (piercing gets tagged onto things that are 'too good'- bows/archery, the one simple weapon that gets reach [long live the long spear], the one 18-20 weapon rogues get [rapier], etc.).
They couldn't get rid o bludgeoning weapons from simple weapons because... well, this very discussion- it would be too hard a nerf for simple weapons since skeletons are common enemies.
So instead, they just removed most slashing weapons from the simple category- slashing tends to have the stuff with great stats, like the kukri, the falchion, or the greatsword.

HenshinFanatic |

One of these upgraded with holy, bane (undead), as well as ghost touch. Alternatively, a +2 Ghost-Touch Disruption Amulet of Mighty Fists, for the lolz.

DanEvans |
This may not be thematic enough for you, but when I ran my Undead Hunter Ranger, I used a +1 Undead-Bane Holy Longbow (after all, pretty much all undead are evil). Depending on your level it is a little pricey at 32k, but if you need a cheaper version drop the holy enchantment which is a +2 bonus, and the bow then only costs 8.3k gold. At level 11 my Ranger was doing 1d8+9 plus 2d6 vs undead and 2d6 vs evil per arrow, and with manyshot and rapid shot, it was firing 5 arrows at a time.