It all depends on your other gear and what you're fighting. Dread venom striker is probably the strongest sword if you have deadly shadow cloak, as attacking afterwards with max damage can deal a huge amount very quickly due to the way that resistances work, but that's more of a speed based tactic.
Acheron is probably the strongest if you're fighting anything besides fiends and undeads, with combuster being the best for undeads (or FoV, like Bopp said, if you have fire resist and won't die from it) and final flourish for fiends.
If you're fighting the roarmulus twins, Divine Avenger is the best.
If you're fighting a mix and have some CTR, troika charges can be quite overwhelming too against many enemies.
Your best bet would be acheron+combuster though.
It depends on the enemy, of course. It also depends on what UVs you are able to get, and even on your defenses. For example, Fang of Vog with CTR+6 and lots of fire protection is pretty powerful.
You might find my detailed sword guide helpful. You might also want to check out the Lancer Knightz sword data directly.