Lets see:
DM/Electric - decent resists (including psi), endurance drain resistance, unlimited endurance late game, slight built in +rechange buff, slow resistance, damage aura, an alright heal\regen, alright teir9 if you really want it.
DM/DA - decent resists (including psi), endurance drain resistance, unlimited endurace mid game, damage aura, a KILLER heal, fear aura, disorient aura, and a VERY useful tier9 self-rez.
If it was me, I'd go DM/DA as a first brute. DM can do well with both, but I personally LOVE me some dark armor (I have quite a few /dark and /elec brutes). Both armors are good, but dark armor has a lot of utility in it that I like.
The Porcelain God - DarkKinetics Corruptor
Meat Juice - DarkDarkSoul Brute
Pretty and Strong - Do you really have to ask?
DM/DA: Started off slow, and grew to be better. With IO's, became an unstoppable monster. My current main, runs missions at +3/x8 since slotting Cardiac Radial.
SS/Elec: Offensive juggernaut. Incredibly hard to kill once Energize was added. Able to run at +1/x8 with blazing speed (2 minutes per mission if I focus).
Try them both! 
My guides:Dark Melee/Dark Armor/Soul Mastery, Illusion Control/Kinetics/Primal Forces Mastery, Electric Armor
"Dark Armor is a complete waste as a tanking set."
Of the two, what are your experiences with either armor in how tough the set was? I'm looking at making my first brute a DM/(Elec,Dark) and would love some input before I take him all the way. Any and all comments/experiences are welcome and appreciated!