As long as your upgrades increase the overall armour rating, the various biases should usually tend to even out.
Enchantments are a little limited from about level 12-13 when you start getting equipment with enchantment slots, up until the high teens or early twenties, when you take over the battle tower and have easy access to enchantment (and potion) ingredients.
With my ranger in DKS, at the end of the D2:ED section of the game, at level 37, my melee / ranged / magic resistance was 22.1 / 38.5 / 37.2. At level 24 I learned Splitting Arrows (should have tried it earlier), after which my melee resistance wasn't a big deal, since that skill was pretty much a die button for normal opponents in melee range.
