To summarize what Meeky is saying.
-None of your battle brothers can do every job well, that’s why we get 12
-Decide early and specialize your guys for their intended roles
-Melee tanks, 2-Handed death dealers, Crossbowmen (not archers) and second line melee. You’ll need them all.
My own rules of thumb
-have 3 brothers to fill each role
-make crossbowmen proficient with 2-handers so using Quick Hands they can defend themselves
-between 70-80 fatigue is a good level to maintain for everyone except for your tanks, they’ll need more for the Shieldwall
Just my two cents.
One of my favorite builds is a 2-Hand sword wielder in medium armor with Battleflow and Bezerk, high attack (80-90) high initiative (100+) and low defense (0-15). He waits until the end of the round to close with the enemy and then at the beginning of the next turn can take 2 sweeping attacks before the enemies do anything. His ability to reliably kill 3 enemies in 1 turn before they can act means he doesn’t even need melee defense. And if he does get hit, the medium armor will shrug off 2-4 hits anyhow.