from optimisation perspective, i think Fire/ignite is the best effect out of all, as it paralyzes enemy for few seconds and deal the damage during same time.. Poison doesnt do that, it only damages health. Freezing stuns the enemy, and makes him slower, while stagger just stuns it.. so overall, burning damage is most effective (enemies are burning until you hit them again, which resets things.. but up till that point they wont hurt you... while poisoned enemies will still fight)
