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.