I'm not overly concerned with armour class, since my hero is a ranger, and have traded an armour class 13 breastplate without bonuses for one with an armour class of 10 and a few bonuses. With my DK warrior, I'd take the lower armour class belt / amulet with better bonuses if is just a difference of a couple points.
I's suggest you swap equipment and play for awhile. If you notice that your characters are taking more damage with the same monsters, swap them back.
When I get some items with charm slots, I am planning to use a couple vitality charms, them strength / agility for my warrior. With my ranger I'll skip the vitality, and probably go with more agility than strength.
