The most valuable traits are the ones that can’t get gotten any other way.
Parkour expert, for instance, gives you a fairly nice bonus (nothing massive, but really useful for kiting) that cannot be gotten literally any other way. Strong genetics is another REALLY good one like this. Strong back/packmule are, IMO, pretty weak (quality of life, not much else), but they do go in here. Weak scent goes here, but it’s really not that useful past the early game. Light step DEFINITELY goes here, and can be a real life saver in night raids.
Night vision is stupendously nice, but for quality of life, but also for surviving on night raids, so it’s REALLY good early game… but it can be acquired fairly easily by mutation or equipment in mid game, so if you’re trying to optimize for late game, it’s not a good choice. (I usually take it anyway.) Most of the traits martial arts are in this category, too, though they can be REALLY useful (as actually finding any one book is rare).
That’s how I think about it, anyway.