I got Elemental Potency as was required for Twin Souls and I'm curious as to whether the Storm Atronach or Dremora Lord is more powerful, I'm having a hard time figuring it out and the Talent simply gives a vague "Atronachs are 50% more powerful" as a description.

Dremora lord is more powerful in most situations.

As a primary Conjuror, I use them both regularly. Or together as the situation demands.

atronach is weaker, but with atronachs you can spam your destro spells of equivalent element without damaging your summons

I don't really do much destruction, I dual-wield bound swords.

I use them situationaly. Obviously, a Dremora lord isn't good at fighting dragons or crowd control, but the antronach is (because of its ranged attacks and electro-cloak, respectively.) Whereas I find the dremora to be better at taking down a single, ground-based target.

Then use lords unless the mobs are out of reach.

Dremora lord just kicked Frost Troll ass. He didn't even take a hit.

Dremora is better. Storm is good has ranged spells.

Get element branch anyways. Lv 100 your able to summon two of anything. Either using two thrall storms or deadra constantly.

I use the storm against dragons, and the Dremora lord against everything else.

I like the dremora lord just for the great voice and lines, conveniently enough they're also total wrecking balls.