Go with fire for sure. Lightning pulls up at second best, but by the time you unlock the third skill in any class you'll already be close to being able to change the main character. Fire is best for low levels because of its variety, dps, and debuff usage/control. You could go the control route and debuff/sleep/seal the enemy to death, or just go damage in general. It's kinda squishy but whatever lol
Once you get to higher levels fire isn't necessarily the best, though