These are my opinions on the different whispers--others may have different opinions.
Madness:
- Existential Barrage (simple): unusable without using choirs (you cannot be within 1" of an enemy if you're not in base to base).
- Terrible Truths (basic): insanity is a strong condition. However, most models have a 7+ or better intelligence which means without choirs this is going to fail to land more often than not.
- Psychotic Lure (basic): situational. It can be good, but it needs a lot of things to line up.
- Cyclopean Gaze (double): unusable without using choirs (you cannot be within 1" of an enemy if you're not in base to base).
- Craven Howl (basic, continuous effect): not good enough to waste activations on.
- Unrememberable Utterance (simple): seems good on paper, but is hard to set up in a meaningful way.
Delusion:
- Spatial Psychosis (simple): the universally good whisper option, generally always useful.
- Seen Unseen (basic, continuous effect): can be annoying, but situational and "meh" at best.
- Ghost and Shadow (basic): can be "useful" if you have a lot of backstab weapons or want to turn off Overwatch. However, spatial psychosis is better at turning off Overwatch. Pretty situational.
- Deceitful Thoughts (double): can be good. However, most models have a 7+ or better intelligence which means without choirs this is going to fail to land more often than not.
- Suicidal Embrace (basic): can be good if your opponent has a lot of scary melee models. However, most models have a 7+ or better intelligence which means without choirs this is going to fail to land more often than not.
- Opprobrious Curse (simple): it's ok at finishing off people that have already taken flesh wounds (making it more likely to succeed). It's also one of the few whispers that can grant experience.
Darkness:
- Cacophony of Silence (double, continuous effect): can be useful if you can spend a double action to cast it. Loses power late game as people get better ballistic skill.
- Penumbral Mirror (basic): useful for moving ghuls around if you can satisfy the casting condition. It pretty much requires wyrms to use. It can be pretty strong if you can get it off.
- A Perfect Void (basic, continuous effect): if you're within 10" you're probably within a weapons short range. If you're standing in the open such that this does something, have you tried not doing that?
- Eternal Slumber (double): usually a "win more" action. It can be good for cleaning up a webgun's handy work. It's also one of the few whispers that can grant the caster experience.
- Cloak of Whispers (basic, continuous effect): if you're not playing with tactic cards, then it does nothing. If you are playing with tactics cards it doesn't do much.
- Sight Blight (basic, continuous effect): it's not entirely clear how this works (or ever worked). Do you need to do per model book keeping for who is an isn't revealed as people enter an exit its range? Pitch Black was replaced with Visibility(x), do you need to roll on a table to see what range it applied? (I would rule it as it always applies the old Pitch Black range of 3".)
The Short List:
- Spatial Psychosis
- Terrible Truths
- Penumbral Mirror
Everything else is pretty niche/situational.