My Tried and True Surge Build
 Psyker Build - Warhammer 40k: Darktide 

Build I've enjoyed using and have done very well with on Auric/Maelstrom for a while now that has left me satisfied. I'm not exactly a min-maxer so I'm sure there's room for improvement, but it suits how I play just fine.

Shriek, Illisi, and Smite for crowd control, Surge/LMB for ranged, specials, elites, and bosses. Taking advantage of the Unyielding damage boost, surge can easily outdamage all your teammates against a boss, unless they actually know what they're doing or have a good monstrosity killing build. It's overall good consistent damage, even if you won't melt a boss in seconds... weakened variants are a different story.

Keep spamming surge on a horde of crushers and maulers, or use smite, and none of them should be able to one-shot you or your teammates.

Use smite or surge to get a mutie to unhand your teammates or stunlock them.

Use smite on hordes to charge your peril to about 100% then shriek towards as many enemies as possible.

For the Illisi, charging it and light attacking twice before recharging seems to be the best strat. If you get a kill with the first charged light, the next attack will be a guaranteed crit that will increase your warp damage, speed and toughness, making it a quick and powerful 2-hit combo especially against groups.

Staff LMB can shred hordes decently and suppress most enemies with enough shots, and synergizes well with the surge staff crit bonuses, but is not a focus for me.