I'm kinda torn between the two swords, since they deal similar damage output when their charges are used appropriately. However, since I am now at the point to choose one of them for my SL runs, which of the two should I get?
DA vs CIV
We need to know
* against which missions/monsters/etc. you plan to use the sword,
* how much CTR, ASI, and damage bonus you expect to have,
* whether you mainly charge or mainly regular-attack
You see, these swords are completely different. They are comparable to each other only in certain tactical situations. For example, CIV is normal with a low-knockback charge, while DA is elemental with a high-knockback charge.
If you're looking at CIV, I hope that you're also looking at Fang of Vog, which completely outclasses it (except for one pesky detail).
"they deal similar damage output when their charges are used appropriately."
What about swing style, normal combo damage, type, etc. If we're only judging charges, get a FOV or Blitz.
As Aureate points out, the various Shadow Lairs require completely different equipment. (See the wiki page "Shadow Lair".) For the Shadow Royal Jelly Palace, for example, CIV and DA are both pretty weak swords. Did you mean Shadow Gloaming Wildwoods (Snarbolax) in particular? And what about my other two (really elementary) questions? I suspect that you don't really want help. Have a nice day.
All SLs will require different gear. DA is more versatile and helpful in most of them but that doesn't matter if you suck with it. The fact that you ask this question shows you haven't done any research and probably assume "if I can beat vana then i can do an sl." That statement is false. I suggest listening to bopp and possibly even watch sl runs on YouTube.
Besides you only get access to Higher SLs if you beat the previous ones.
Darkfire Vana...
I mean, that's the only logical explanation for it. Hurr durr.
Rabid Snarby...
I mean, that's the most popular SL with undead. Hurr durr.
CIV is terrible. Don't use it. It's as bad as Wild Hunting Blade.
DA is generally considered to be superior, since the damage bonus vs. undead becomes redundant if you're maxing out sword damage, and you get a bonus vs. constructs as a result of its split elemental damage; its one drawback is that its charge vanishes if your back is against a wall. The multiple projectiles still form and do their initial damage; it's just that they vanish instead of flying off with your opponent.
CIV is generally considered to be less irritating in parties than its cousin the Leviathan, given that it doesn't send stuff flying all over the place. Its charge also does lots of damage against turrets, heavy enemies and cornered enemies, due to its multihit nature. It looks badass as well, but even so, I'd still get the DA first personally.