These passives will be ordered alphabetically. I’ll leave it up to you to decide which ones are the most important, but on higher difficulties you definitely want to focus your passives on making your characters survive better.
Backstabber: Reasonably good if paired with the first level of the throwing skill, which essentially makes this passive a free damage boost.
Dodge: This halves the enemy crit chance. Super important.
Evade: Extra ranged damage reduction. Archers are a PITA. Get this.
Fencer: This makes you less vulnerable when flanked. You could just avoid being flanked, but the way battles sometimes start actually makes that unavoidable. Good passive to have.
Fortune-favoured: You don’t get to increase your stats after creating a character, only your skills, and this essentially gives you three extra points to finesse. It’s pretty good especially on your damage dealers.
Hardened: Extra hitpoints, you should get this on every character you’re going to take into combat without question.
Keen-eye: If your character can take this passive, he should. Part of the reason why bowmen are so nuts.
Low-profile: Halves the chance of the AI deciding to target this character. Completely ignore this passive on your beefy guys and prioritize it on your archers and supports.
Night-owl: Extra mental resistance, important for your archers but not really for others.
Night vision: Again you want this on your archers and that’s it.
Nimble: Having this means you can equip a higher tier of armor without noticing it. That’s pretty sweet.
Opportunist: The AI really tries its best to avoid attacks of opportunity, but I would still get this on your frontline guys.
Quick Feet: Worth considering on dual wielders.
Strider: Extra movement point. Less important for archers than it is for your melee dudes.
The other passives aren’t all terrible, but these are the ones are much better than them.