As far as I understand it's basically a bonus or penalty to your attack roll, the same way tool quality affects other jobs, such as e.g. skinning.
If that is correct, you should probably use a combination of the right tool for the job (i.e. different weapons for different armor and defenses), and the best chance to hit. This, however, usually boils down to the weapon you're the most proficient with, as your skill with any secondary weapon is probably a lot worse, even if it isn't very suitable for the target (a poor hit is still better than no hit, and a hit that doesn't cause injury still damages the armor, which will eventually break when damaged enough).
Also note that it's at least as important to reduce the other skill roll penalties, i.e. encumbrance and fatigue, as they have a tendency to far exceed any weapon bonuses/penalties if not kept in check.
It's great to have such protection that nothing except a very successful hit harms you, but it's not as great to have your chances to hit reduced by 30% due to the weight of the armor, and every attempt to attack (with that penalty) accumulating an additional 2% fatigue penalty on top of that.
At a guess, combat is "VERY HEAVY" work.