Finally got my Krogan Battlemaster. Any advice on which would be better power option, Carnage or Barrier?
Somebody may be able to respond with more authority, but I went with six in everything except carnage and carried around a GPS following this build.
Murder Train:
Biotic Charge: Force and Damage (4), Melee Synergy (5), Barrier (6)
Carnage: N/A
Barrier: Barrier Strength (4), Shield Recharge (5), Barrier Strength (6)
Krogan Battlemaster: Damage and Capacity (4), Power Damage (5), Weapon Damage (6)
Rage: Melee Damage (4), Martial Artist (5), Fitness Expert (6)
Basically, your goal is to play conservatively and get your rage on. Then, heavy melee into everything. Keep barrier up forever and if your shield drops, biotic charge to refill it. As long as you don't jump right into a group of people, you'll do well.
Unfortunately, and this really sucks because it's how Krogan are pretty much based around (i do pretty much the same thing with my Sentinel and it rocks), Rage is broken on the Battlemaster.
I don't recommend putting points into carnage as an armor boost, depending on enemy type, and melee is going to output way more damage than you would using those points to boost carnage. In addition, you'll want your cooldown up for for Charge so you can restore your barrier.