I have to throw my hat in on this one, I would say Elec melee/FA. I have one at 50 (a brute) and between thunder strike with a +rech Io and Lightning Rod with a + rech IO it tears through fire farms and pretty much anything else with ease. Currently sitting at 52% def to fire/cold, other def at or above 45%. I cannot remember the last time I used an inspiration on him....
Another good combo would be TW/Wp or TW/Inv. Abuddy is having fantasric results with a STJ/WP scrapper.