Material is the primary concern with armor. If your options are an iron legging or bronze greaves, the greaves are most likely the better choice, but just about anything will pierce copper.
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In a match between 2 humans, both wearing the typical AI militia uniform of an iron breastplate, helm, and shield, with competent axe user, fighter, and shield user skills, and the only variable being one team has silver battleaxes and the other bronze great axes, the battleaxes win most of the time. This is a sample size of about 12 fights, though, with 1 initial fight being won by a great axe user who then escaped her cell and beat the crap out of another opposing team member after her fight, before being taken down by a third. That was the only victory, but this isn't particularly well-planned experimentation here.
I always thought my silver battleaxe adventurers kicked a lot of ass. Most opponents are lightly armored, anyway, so the fact the silver can't penetrate any decent armor materials rarely actually matters and it's weight obviously improves it's blunt options significantly. A breastplate and helm are about all AI military members will wear on a regular basis, and those only protect the torso and head. Anything else is fair game, if you can get around their shield. Looking at the combat logs, this is exactly how they're killing each-other. The silver battleaxe users have a greater average speed than the great axe users, probably because a great axe is so damn GREAT, and that's probably the big advantage.