so the best way i have seen Poleaxe done right in D&D is as such
Poleaxe 2h exotic small: 1d6 medium 1d8 large 2d4 crit x3 type piercing bludgeoning or slashing
because of the poleaxe's design an attacker must declare which type of damage they are using B,P,or S for the perpous of damage...