"Mace" is not just a different name for pepper spray. Mace is actually tear gas. But it's confusing, because there's a pepper spray manufacturer in the US called Mace Security International.
The effects of pepper spray are really nasty, but one disadvantage is that it must be sprayed into someone's eyes or they have to inhale it directly for it to take effect. On the upside, it's more effective than mace when used on people under the influence of drugs or alcohol (because it doesn't depend on a pain response), and also wild animals.
In Queensland it's not legal (for civilians) to carry mace, pepper spray or capsicum spray.