Currently, I have calibur and flourish. However, as buying a 3* armor few days ago, I wanna move on to 3* sword.
I heard a lot of peopl choose tempered calibur but since I hardly encounter shadow resistent monsters and alreay have a flourish, I am considering a nightblade.
Which sword shall I choose?
Current Loadout
Sword: Calibur, Flourish
Gun: Firotech Alchemer
Helm: Skelly Mask
Armor: Scary Skelly Suit
Shield: Defender
Except if you are soloing and want to keep Calibur for its charge at all cost, you should switch to Nightblade (or any elemental brandish would work too). With 2 specialized swords, you'll deal bonus damage against 4/6 families and normal to 2/6 families. With your setup, it's bonus against only 2 families and normal against the rest.
Eventually, you'll want to have 3 specialized swords (elemental, shadow, piercing) and take 2 according expected mobs in the level.
Just as a side-note, your helm, armor and shield are sub-par choices. This is not the object of the thread and there are tons of threads talking about it, so I'll not develop on this.