Absolute best Skitarii build (use auto tag with auto special tagging!)
 Skitarii Build - Warhammer 40k: Darktide 

EDIT: Finally I've gotten around to publishing the auto tagging mod I've written. It's called `Auto Tag Survey` on nexusmods (can't link URL here)

So I've arrived at this build after a bit. I really do enjoy the passive toughness regen. It helps a lot. Skit is generally, especially in havoc 30+, pretty squishy. This helps you soak up being hit by horde type enemies from time to time and such but in general, if you get hit you go down as easily as vet or scum. Your toughness regenerates quickly though, you buff up your team, it's great.

Weapons

Mechanicus Power Sword:

So, PS got an a huge buff when they simplified the rotation. Into hordes it's push attack light heavy rotation. Or just light spam. Single target is generous -> either h1, l, l, l, h1 or anything but the sweeper heavy. i like l, l, l, h4 a lot too. Special hits like a truck as well. You've got a lot of crit, this weapon loves to crit and hit weakspots. Does boatloads of damage to bosses or anything in general. You're running 80 mobility which gives you 4 dodges, it's a must, makes the weapon feel way more mobile.

Phospor blast pistol:

Infernus + surgical helps you stack 16 fire onto bosses which then melt, your skull keeps the stacks going, it's really just a lot of damage. Bosses melt. Great into gunners as well.

Your most important ability here is noospheric. With auto tag mode with survey mode (auto tags specials) it just dishes out so much damage. Now that it's been nerfed and you can't spam it with no capacitance, I've opted for picking up capacitance gain nodes which are enough to keep you topped up even after you use an ability.

I could go more into depth regarding other nodes but generally, you're a melee power house with fire stacks through ranged. conserve your ammo, especially in havocs. you can get hit and you regen toughness quickly but if you get hit multiple times in a row you die, you don't have the health nor do you have a lot of toughness so take care. The newly improved mobility of PS though + 3 12% stamina regen curious give you a lot of pushes and dodges. Use them, they will keep you alive.

You're a boss killer, you eat specialists for breakfast, you're decent into hordes. Just overall great allrounder which helps eliminate threats quickly while buffing your whole team and auto solve minigames. What's not to love?

NOTE:

In havoc, if you have goop (blight spreads) I recommend picking up Ablative Wards instead of Adaptive Combat Calibration 

also Adaptive Combat Calibration is in general a flex node for me. Flux Conduit Build-Up, Evasive Servo Recovery Adaptive Combat Engram Assassination Protocols are all good