As of now, I'm planning on having Gran Faust, Argent Peacemaker, and Electron Vortex with Vog Coat, Barbarous Thorn Shield, and Divine Veil. This gives me a sword, gun, and bomb as well as a weapon with good effectiveness against anything other than Beast (and sort of constructs since Electron isn't a damage bomb). So, with that in mind, I wanted my last weapon to be good with Electron Vortex (which means it has to be a sword or bomb, but I prefer sword) that is good against Beasts and maybe Constructs. So, here are the weapons I was thinking of:
Wild Hunting Blade
Barbarous Thorn Blade
Final Flourish
Fearless Rigadoon
Furious Flamberge
Combuster
Voltedge
Glacius
Divine Avenger
The five top ones are good against Beasts either due to beast bonus or piercing. The lower 4 are good againt construct because they are elemental. Now to narrow the list down. From what I can tell, the Flourish's charge attack doesn't go nearly as well with Electron as BTB does. Next, since I will usually use the sword together with Electron, Glacius and Combuster are better than Voltedge. Then I decided to list the pros and cons of all of the remaining weapons.
Wild Hunting Blade
Pros:
Since it deals normal damage, it doesn't need as good a UV to still damage constructs decently
It has a 2 star version so it is easy to get UVs for
Cons:
Since it's speed is already high, Vog and the ASI trinkets I want to buy don't help it much
Its overall power is very low so it doesn't deal much damage to mobs
Its charge attack lasts a long time so it can leave you vulnerable if the Electron Vortex fails to shock enemies
No status effect
Barbarous Thorn Blade
Pros:
Pretty good damage
Its charge attack has a little bit of range, which is always handy
Due to being pure piercing it deals very large damage against beasts
Cons:
Pure piercing means it deals such pathetic damage to construct that I can't use it for them
No special effect
You start alchemizing it at 3 star, so its fairly costly to get good UVs
Divine Avenger
Pros:
Very good damage
Due to having split elemental and normal damage, it deals good damage to Construct while being usable against Beast
Its charge atack has range
Cons:
I'm pretty sure its charge attack will never hit enemies in an Electron Vortex more than once
No special effect
You start alchemizing it at 4 star so it is very hard to get good UVs
Combuster:
Pros:
Pretty good damage
Due to having split elemental and normal damage, it deals good damage to Construct while being usable against Beast
Fire lets it deal damage over time
Pretty good damage while still having decent speed
Its charge attack works well with Electron Vortex
You can start alchemizing it at 2 star, so you can get good UVs without too much trouble
Cons:
None that I can think of
Glacius:
Pros:
Same as Combuster, but deals a bit less damage in exchange for being easier to chain enemies with it and Electron
Cons:
None that I can think of
So based on that, it seems like Divine Avenger and WHB have more downsides than the others so Glacius, Combuster, and BTB seem like my best bet. At first, Combuster and Glacius seem to far outclass BTB for my situation, but I should end up with more trouble against Beast than I would Construct, so BTB is still a choice. So my question is basically: Do Electron Vortex, AP, and GF handle Constructs well enough that I should go with BTB, or would it be more beneficial to use a 5 star Brandish with a Beast UV? And, if the Brandishes are the way to go, we come back to the ancient question of Combuster vs. Glacius.
Will come back to read your wall of text for a more thought-out reply, but I had to ask you something first.
Why carry AP for general purpose? (I'm assuming this isn't your fsc gear since you'll be using a barb shield)
It takes up a slot that is only against two mobs, undead and fiends. It is barely good against devilites due to their dodge, and greavers are best dealt with swords. It will also not do well against polyps and gunpuppies.
Gran faust is fine against beasts since shadow damage is neutral against them.
EDIT:
So first off, unless you have a good CTR UV, or two ctr trinkets (which is a waste), it could be difficult to lay an electron vortex, charge, then attack. At least, this sort of damage won't be efficient. Although, I don't have this bomb, how easily can you lay the bomb then charge your AP? This will allow you to see at what point you can release the charge during the bomb's vortex on a normal sword. The gran faust's charge is far too long, so don't use it to test your strategy.
In my opinion, you would be better off laying the bomb, switching to the sword and dealing normal swings for high damage to a condensed group of mobs. You would be able to get off several swings. For instance, with your gf, you could swing-shield-swing-swing for the most damage before the vortex disappears.
Given this, I would recommend the DA as your 4th weapon.
My friend has an electron vortex. The combination of his vortexs with my DA destroys slags very quickly in FSC. Further to this, the DA charge will hit the slags multiple times since it will push them out of the bomb slightly, with a few being tossed out, and the rest snapping back in, only to be tossed out by the bomb. It's a mess of numbers, so it's very hard to see since I don't normally look out for it. If I'm not charging, the DA's second swing is very deadly against a group of mobs in a vortex. The knockback is useful to clear the area so we're safe.
Second, I recommend the DA because you have your gran faust. If you like the 2-swing swords more than 3-swing swords, I say you should stick with what you like. This let's you get used to 2-swing swords way more and use them effectively. By having one shadow and one elemental, you ensure you can damage everything at lest normally. GF will deal decent damage to beasts, elemental will deal decent damage to fiends.
Lastly, you may want to destroy turret mobs from afar, and the AP will be weak against two of them. (Although the damage is mixed, the numbers seem to be penalized even more than you would expect. I don't recommend this gun for general use) The DA will make up for that with its charged attack which can hit from a distance and does very good damage.
The glacius & combuster, though good, will not be good choices since:
a) your won't be charging into your own vortex unless you have a good ctr.
b) the normal swings are too narrow for attacking a cluster of mobs in your vortex
c) there is no knockback, which sounds important for the type of strategy you're trying to execute
d) you already have shock status from the bomb, this offers damage over time and some crowd control already