The critical imbuement can help you to kill more faster, so reduce the time who you confront each creature (Also up the experience/time).
You have to consider that vampirism can be used on the armor too, but critical can only be used on the weapon. Each of imbuements are totally useful and gonna help you to make more profit, experience, less waste, kill more faster and get more survive.
So at the end in my opinion, get critical and void on the gnome sword and vampirism on the armor.