Really it depends what your main character does and how you want to compliment there abilities.
Eder - Since he has Knock Down even if you respec him I like to tank with a guarding weapon plus shield and take the Overbearing Guard ability. Give some damage+accuracy and not just every tank ability+trait so he hits hard if opponents disengage.
Maneha - Since she has Barbaric Yell I tend to go more off tank + aoe. Weapon + Bashing Shield with Heart of Fury later. Abilities like Savage Defiance, One Stands Alone, Thick Skinned, Threatening Presence, Dragon Leap and Echoing Shout so debuffs and aoe damages groups. Very similar to The Golden Dragon
Kana - I like him also as a tank so he is in front line using a build like Drakes Ambassador to use his Might + Int. Bit squishy so early on i'd focus more on defense traits. Plate armour and defensive rings etc so he survives whilst letting the basic endurance drain chant work (front line so should hit lots of enemies and armour attack speed pen doesn't slow the chants down) then use paralyze/charm invocation. I think if going ranged the chants like ranged attack speed can be nice with ranger etc but I find other ranged roles more interesting.
Pallegina - Very generic attributes, I tend to add her if melee heavy to buff those around her like The Rauatai Captain
Zahua - TBH I don't use very often since I find monks micro heavy but could use a build that just stacks wounds (Turning Wheel + Iron Wheel) or switch AI on. I tend to go more off tank since he can move / displace opponents to help protect companions. I like fists just for RP reasons.
Durance - Standard priest, I give him a weapon+shield just to deflect since most of time he will be casting spells from middle of the group. Can do Fire Priest which fits Durances character.
Sagani - Fairly standard ranged damage though her DEX is low so want a good item to buff that so build like Storm & Plague Caller.
Hiravias - With a mix of attributes and Heals, CC and Damage spells can do pretty much anything. I tend to use him as utility to add whatever is needed.
Aloth - Again a mix of attributes but good dex+int to spam spells. I focus on CC + damage back line.
Grieving Mother and Devil of Caroc I never really use. Both are really damage roles but attributes aren't great for it IMO.
For example my current game I have a ranged cipher as main damage dealer with CC.
Durance is main healer + buffer to protect against paralyze etc.
Eder is main engaging tank.
Maneha is off tank debuffing + aoe.
Last 2 are typically 2 of Aloth, Sagani, Kana (as another OT in wide open areas) or Hiravias. Mostly want damage and secondary heals/cc to round out the group.