I find the mace to be a better pick because of its high amounts of stam on it.
Title says it all, I'm a DK tank and have one and can figure out wich is better.
Lightborn Spire - Item - World of Warcraft
Quel'Delar, Ferocity of the Scorned - Item - World of Warcraft
According to the comments on the mace ending quest on wowhead:
A Victory For The Silver Covenant - Quest - World of Warcraft
Classes which can wield swords are not given the option to take a mace reward instead.
Cold Comfort: Rational Cynicism in the World of Warcraft