Dwarves versus Orcs.

First of all: don't use Chaos against Orcs... If they have a non-zero initial Fury, it will absorb a lot of damage.

Here, the question becomes more interesting: what is more important, 1) preventing the Orcs from accumulating Fury and becoming killing machines, which would require your units to focus on reducing their Fury, or 2) strengthening your own units so they can fight equally well in melee combat? The first can be achieved with area-of-effect spells from Chaos (since there's plenty of magic available), and the second can be achieved by buffing your own units.