For death animations? I doubt it.

I was more inclined to mathematical calculation. For everything else, there's a MasterCard.

lol Corbo'd
Now on topic, I think the percentage system is better because... I don't know, I like it best.
But, really, the +X system is much easier to comprehend, and you won't be having to do mathematical calculations to get the actual damage you're dealing. Just for the record, I don't want to start a discussion about someone being too lazy (like me) like to do simple percentage operations.

I prefer the percentages. They actually take into account how much damage the unit would do normally. Instead of having it like SC 1 with the best being all of the damage going through, there should be a bonus against certain targets and a deduction against others, like it is, just not one set bonus or deduction, like it is.

Not only that, but you can stack both variables together.
For example:

Dark Templar,
Normal Damage
Slice Damage
Normal Armour
Flesh Armour
Shields

Versus

Ghost
Concussive Damage (right?)
Bullet Damage
(Heavy?) Armour
Flesh Armour

Concussive > Flesh
Slice > Flesh

But if you had say a goliath with Metal armour, Slice would be ineffective, concussive would be minorly ineffective (canister shot, it hurt).
Different epic usages.

The Ghost will go under the "Light" Armor category...

+dmg vs %dmg is technically the same number represented in a different way. +dmg is just faster to comprehend because you only have to add, not fractionalize for percentages. You must take more mental steps to figure the result of a % system versus an addition system.

For instance, a Vulture in SC1 did 20 concussive damage. Expanded, that's 20 to small, 10 to medium, and 5 to large targets.
- The Ghost did 10 concussive damage. That's 10 to small, 5 to medium, and 2.5 to large targets (decimals now, eh?).
- The Siege Tank did 30/70 explosive damage. Quick, what's 75% of 30?

The Siege Tank did 15/35 to small, 22.5/52.5 to medium, and 30/70 to large targets. Care to explain how that is easier than the new system?

Another disadvantage of the SC1 method beyond player comprehension is balance. The designers have a lot more flexibility with this new system, as they can give the Ghost +20 damage to light targets or +10 damage to light targets without affecting the base damage nor the damage of any other unit. With SC1, design was restricted to applying the same reductions across all units that used that damage type.

Also, I like that there are only two unit types (Light/Armored). Warcraft III was horribly bogged down with overly complex, obfustificated armor/damage relationships. The further away from mechanics that are not visually represented, the better. Compared to Warcraft III, SC1 was tame and only utilized damage modifiers where important (rather than base the entire game around them).

Concussive:
- Firebat to restrict the usefulness of his splash on targets outside his realm of specialty.
- Vulture to ensure it specialized in early game and harassment tactics.
- Ghost to limit its damage potential as a caster (one of only two casters that kept their attack).

Explosive:
- Dragoon and Hydralisk to empower small melee units as an appropriate counter.
- Siege Tank to keep effectiveness against buildings/defenses without totally overpowering it against small units (who usually don't have many hitpoints to begin with).
- Arbiter to limit its damage potential as a caster.