Out of "Dark, Elec and Energy"
Energy can be more scrappy/brooty
Elec might be better on a Tank, a bit squishie on a Broot (it is epic looking but meh at the defeating)
Dark can be build to 'look' like it has good numbers but ranged, debuffs, and the stunning synergy could be considered lackluster..
alternately:
EM/SR & EM/INV can provide some interesting proccing & slotting opportunities.
EM/FA can build some good damage