mediocre to low ee --> chains/plates
high ee --> scales/leathers

plain mathemathically u get way more physical attacks than magical. also magical attacks have a much higher chance to crit. crits ignore the def. so vs a lot magical attacks it doesnt even matter how much def u got. so in the end moast attacks def is effective against is physical def. try to cover this first and when u have the funds look to cover some magical attacks as well.