Potions
Store them in the bank. Take em when you need em
The potions are more for when you know what you are going to be doing beforehand, such as dungeons or a map you’re familiar with. If you have to choose between the two, the sharpening stones are more practical overall. If you prefer to min-max, you’ll need to see how much damage you gain from a sharpening stone yourself, and compare it with the potions.
I prefer to haul like 12 different potion stacks myself. It’s even more practical, especially being able to share with the rest of the party that hasn’t brought any Nightmare Court slaying potions.