Skolver Set versus Vog Cub Set
In general, which is more preferable for general exploration- Skolver or Vog Cub?

It depends on what you have as a weapon- Skolver is better for faster swords, and Vog is better for slower swords. That's because the lower the sword's speed, it seems like the speed boost is more noticeable...
If you use a mid-speed sword, or something other than swords, it's best to get what you're going to need most. Running JK? Get Skolver. Running Firestorm Citadel? Go with Vog. If you're not going to consistently run either of those, I'd go with a combination of both.
I plan to be using the Brandish series- eventually Acheron. Would that be considered a fast sword?
The Brandish series would be medium speed, so the speed bonus from Vog wouldn't be as noticeable as on a slow sword like Divine Avenger. Even so, it is always nice to go slightly faster, allows you to recover from a swing more swiftly to go into a block or dodge.

Personally I don't see or feel much of a difference with IAS on the Brandish, Calibur, or Flourish lines - I've never had much trouble getting a shield-cancel in time. The difference on Troika or Sealed Sword, though, is a huge lifesaver.

Acheron is medium speed, which is similar to the calibur line (I use the 5*, Leviathan). I recently upgraded to vog cub and the increased attack speed was immediately noticeable for my levi. There are some monsters that I can now use full combos on that previously I would have to hit 2x and shield.
In general, one of each. That way you have a balance of elemental and piercing defense. A balance of freeze and fire resist. And a balance of increased sword damage and increased sword attack speed.