Can some explain which weapons do well against which other weapons?

I know it's complicated, but any tips on how to understand this or other specific resources that explain this aspect of the game would be great.

When is it best to wield two swords, two daggers, one of each, a mace and a sword, etc.? Given armor class, skill %, and hit/dam/ave is equal in all situations, how do these compare?

What everyone else says about hurting your enemy is true. Generally you want to be using something they don't know how to use. e.g. Use swords against conjurers, for example.

However, one thing to take into consideration is the active skills you'll be using. Flurry isn't great against a shaman, in general, because it won't kill them. However, against an elf thief, you might still want to use iron swords (even if they know them) rather than axes, because if you flurry they're quite likely to be toast, since they don't have parry for your active skills.

Having said that, here's my general rules of thumb (and guesses) for which weapons parry each other well:

Spear seems to parry things like axe well.
Axe seems to parry axe well.
Dagger/whip don't parry that well in general, and seem especially bad against axes.

My general rule of thumb though is:
- against "heavy" types of weapon, use either a 2 handed weapon-TYPE or another heavy weapon.
- against a light weapon, consider a sword.

1) Different weapon types are harder/easier to dodge and parry. For example, Flails, Whips, and Daggers seem harder to dodge, while axes, maces and polearms seem harder to parry.

2) Always think about what weapons your opponent can use. When at all possible, use weapons your opponent's class cannot learn. This severely nerfs their ability to parry your attacks

3) Also consider whether you are under more pressure to block their attacks, or to land your own. A sword and shield, or a spear will be better defensively than another combo, but will deal very little damage overall. When you need to land the maximum number of hits, a flail main and axe/mace offhand seem to do pretty well.

4) I am fairly certain weapon types have special interactions, but my opinions on this are just hearsay. When I have played staff/spear specs, I generally felt that spears parried hand/mace/staff/polearm better, and staffs parried sword/axe/dagger/spear better.

Generally speaking, its better to use a weapon your opponent doesn't know than it is to hit a vuln.

IE, I'm fighting a duergar shaman, so I'd rather use a blunt damage steel mace than a holy damage sword, despite it being a vuln. Obviously vuln + doesn't know it is best.

It is going to depend on what weapons your enemy knows. If they don't learn the weapon skill, then you are going to land many more hits. For example: sword and mace might be good against a shaman since you will parry well with a sword and they don't learn how to use maces. If you go against a paladin, replace mace with axe. Use staffs against orcs, most mages can't use swords, stuff like that.