This has probably been said before, but the obvious way to make armor more unique is to have different types of damage, and make different armor protect differently against certain types of damage.
This way, you might have to switch armor depending on what enemy type you're most likely to fight.
It can be different types of non-magic damage (slashing, piercing, bludgeoning, ranged, thrown), magic damage (elemental) or situational (backstab and other trickery) all combined together.
This would also allow to make different weapon types really useful.