What were you having troubles with?
To me, that's a key point. Both /dark (which I have played) and /thermal (which meshes well with demons) are solid choices, and I'm doing fairly well with /poison, but I don't know if I'd recommend that of the three.
50s: Yumi Eryuha-Arch/Energy, Mirria-Thugs/Dark, Meyami Kitsuna-Claws/SR, Celesta Seusen-SS/Invuln, Lady Mirriella-Illusion/Empathy
Arc 503982 "Dimension Xi Epsilon 22-10" Part one of a multi-part arc.
I kept 'losing focus' on the mm's as a concepts and a characters. And so as I'd lose focus they'd be replaced till I found a concept and power sets that 'click' for me. its happend across all AT's but I've found at least one combo that fits with me in each AT. but MM's I haven't placed as much time in so I haven't found a combo that meshes yet for me.
I suggest /thermal. It makes the most of the auras of your big three pets hitting you and the foes. Your ember demon shield and heal overlap the hellfire gargoyle debuff and the demon prince debuffs/slows and also your own PbAoE heal. Your MM and pets will move as a group, you want them in close. Keep the little buggers from chasing to far from the main group.
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
Yeah after my second post here I rolled her as a demon/therm and loving it for the most part.
Have been trying MM's on and off since CoV started but couldn't seem to get any of them past 20. I'm thinking about giving it a go again with Demon and pairing it off with dark, poison, or thermal and having trouble deciding which.