DM/INV and DM/Shield Best on Brutes or Scrappers?
DM/SD is going to be best on a scrapper. They get far more of a boost from powers that give damage bonuses like AOO and soul drain due to their higher base damage and the fact that they get higher bonuses from the two powers. For example, soul drains base damage bonus for a single target is 60% for scrappers but only 48% for brutes. Any damage bonus brutes get is further watered down by combining with fury.
DM/Inv is not so obvious - dark melee will be better on the scrapper but invulnerability is likely to be better on a brute due to their higher base HP and HP cap. I guess it depends on what you want out of your dm/inv character - do you want to be more of a damage dealer or a little more tankish? If the former, go scrapper, if the latter, go brute.
Globals: @Midnight Mystique/@Magik13

DM/SD - scrapper.
DM/Inv - hits harder on scrapper, sturdier on brutes. The combo is arguably already tough enough to survive most of the normal situations and even many ludicrous challenges on a scrapper, so it might make sense to go scrapper and enjoy the extra damage. Then again, the extra survivability on the brute is godlike, the kind of character that can take punishment meant for entire leagues and come unscattered ; that's also fun.
If you're making both, I'd go brute on the inv for sure. Accept the DM/SD scrapper is going to school the DM/inv in damage no matter which AT you pick, and go all out with survivability as to give that second alt a niche.
Im planning to build a DM/INV and a DM/Shield character but cant decide on the AT. Brutes will definitely have an edge in survivability but in terms of damage, Im not sure if they can compete with scrappers who will benefit from the +dam in DM (or shields). DM/INV, in my opinion, would be best on a brute because of DP and scrappers would be better with DM/Shield Does that sound right?