Intelligence to 30 (aside from Ghazwhan and Klethi for me). on all, Trainer to 10. Rest into Strength (30 Strength if you play long enough). Ironflesh, Powerstrike and Power Draw all to 10, essentially makes them durable power house archers. Masterwork War Bow or Masterwork Strong Sarranid Bow and they can wipe out entire armies. I give them Heavy Mallets or Heavy Manhunter Mauls, 2x arrow slots and the bow.
So far it has been the most efficient combo, you can sub with Crossbows if you don't want to take the time to invest in Power Draw. High strength offsets Power Draw penalty from heavy armor completely, so put them in the high tier stuff. Due to poor cavalry AI, they don't do nearly as well on horseback and tend to get mobbed very quickly. If you play 1/4 damage this may not be an issue, but it's a big problem on full damage difficulty.
Alayan: Trainer 10, Engineer 10, Tactics 10 rest into combat.
Jeremus: Trainer 10, Wound Treatment 10, Surgery 10, First Aid 10 rest into combat. Supplement your army with 8 surgeons (bottom of your party list) to help compensate for your lack of the full strength Surgery (10+4).
Deshavi: Trainer 10, Pathfinding 10, Spotting 10, Tracking 10 rest into combat.
Baheshtur: Trainer 10 rest into combat.
Klethi: Agility to 30, 10 Foraging, 10 Looting rest into Strength and combat skills.
Ghazwan: Charisma 30 (companions reading books is broken, otherwise it'd be 26 Charisma, then read +1 Trade book, +1 Charisma book) 10 Trade, rest into combat.
Edwyn: Trainer 10, rest into combat.
Nadia: Trainer 10, rest into combat.
Ymira: Trainer 10, rest into combat.
Bunduk: Trainer 10, rest into combat.
Firentis: Trainer 10, rest into combat.
This combination of companions will always remain Very Happy, no companion conflict. This is obviously a setup for a longer playtime game, as 30 Int and 20+ Strength takes a long time to achieve. Ideally a minimum of 15 Strength is needed for Power Draw 5 and the best armor + Mallets/Manhunter Mauls. Pump strength to 15 early on so they can use Imperial War Bow/Sarranid Strong Bows, which greatly helps them level. With good armor + good bows you can take on 50+ Forest Bandits/Bandits with just you and your 11 companions. Tons of exp. (And that's on full damage settings).
This frees me up to go pure combat Strength/Agility, or Strength/Charisma with maxed Leadership and Prisoner Management.