[thejeff]

Shadow Brand: Larger area, MR resistable. Doesn't work on lifeless.

Frost/Fire Brand. AoE1. Doesn't work on Cold/Fire immune.

Shadow Brand is really nice against normal chaff.
SC's are likely to have enough MR to ignore it. But they're likely to be Fire/Frost immune too. Especially once you start fielding lots of Fire/FrostBrand wielding thugs.

Against standard Undead chaff (longdead/souless), Firebrand is really the only option. Though against truly huge hordes of chaff, damage shields are the only thing that works.
Even with a Firebrand and quickness, 1 SC can only kill 300 human sized units before hitting the 50 turn limit.