well, your choices are either a sorc, javazon, or pally. The main problem with a sorc is that since it only gives +1 skills, you lose out on 2 points in mastery and 2 points in skill, plus the % bonus to damage is added to the base damage before mastery or synergies are applied.
Ive been thinking about getting one for my tesladin. Holyshock gets 1-915 base damage so the 15% lightning damage would add about 140 damage. With my crescent moon phase, i already get -35 lightningn resist so this would add an additional 20? for a total of -55 lightning resist. The faster cast is wasted but all in all it will work pretty well i think.