I have the Frying Pan with 5x Mana augs & M. Crossbow with 3x Mana augs. And you know what? I have mastered everything Will and poured the oversplash ONLY into Guile and Speed. & Thus, my "Genie Rogue" character was born..
So because of my Runemaster's vast recharging aspect, it means attack spells (namely Lightning!) combined w/ slow time end up virtually COST FREE, by the time Ive zapped, clapped or toasted my foes to mere particles!!
So yeah.. From an economical sense, and because of the OPness, It's gotta be Lightning!!
Nobody mentioned Battle Charge? I like to snap onto a foe behind me with an punishing burst, by pushing down > Cam Reset > Charge. Has a nice radius, distance and damage when maxed - not to mention it renders you're INVINCIBLE ( from both damage AND knockbacks!), from when you hit the button, up until you've come to a skidding halt and (most) enemies are on their asses, giving me time to position myself for a Ghost Sword, followed by OP lightning chain, or Enflame..
I should also not omit the fact that B.charge, when timed right, negates even Dragon-form Jack's firebreaths of fuggery! So one can imagine how it can help you EASILY defeat Minion Mages - even SUMMONERS - UNSCATHED!! - simply charge, roll backwards, wait for them to cast their zappy death balls, then charge again!
NOT only will you negate their spell and score a reasonable amount of damage, they will be helplessly stuck in the final frames of their casting animation - letting you pop off yet another attack before you even roll away!
Only downside to B.Charge I've found is in the mistiming vs. late game enemies immune to knockback - Summoners being one of these.. Their melee attack is quick, has good range, does high damage + knockdown, so yeah, it isnt anything to scoff at!
Learn their patterns, time it well, and most importantly - DON'T forget to ROLL AWAY!