NS saves your kill when you have 4 light bolts on their way to the target and he starts runnin los! just pop em ns and hes dead.
sure wrath gives 3 crit/totem but you might just miss the insta cast for the "free" first arena kill.

id say go with wrath totem untill you have 30% crit with gear and talents then respec and try it out.

/stick