The mace is the much better weapon. Strength and Stamina are much better than Agility and Stamina. You will get 168 AP from the mace over the 100 on the polearm. The damage range is higher, all DK strikes work off the damage range of a weapon. 5 expertise is nothing to scoff at either. Overall, the mace is a much better tanking weapon or dps weapon. The armor pen is meh, but more useful for blood spec over frost and unholy. While 40 hit is nice, you will be doing your DPS(and threat) a disservice using the polearm.
Use the Argent Skeleton Crusher until you can pick up a Titansteel Destroyer or a Naxx weapon.