The Arc Knight (possible meta)
 Skitarii Build - Warhammer 40k: Darktide 

This build is at its heart, a hybrid. You want to be actively weaving between chordclaw and arc rifle to get the most out of it. Outside of chordclaw, you will also do substantial carapace damage to crushers after shooting and/or hitting them with an arc four times then swapping to your transonic blades in single target mode.

I believe this build or a variation of it will be one of the stronger Skitarii setups for games with random players. It has extremely solid damage, easy access to brittleness and good ability generation.

Melee: This is up to you. Of Skitarii's unique weapons, the paired transonics are probably the weapon most will feel most comfortable with.
The mechanicus power sword is also viable if you have the hang of it.
arc maul is optional but not mandatory as you get plenty of arcs from your ranged weapon.

For the Paired Transonic blades I recommend extra damage vs flak to amplify the weapon's damage in its single target mode, and extra damage vs carapace to shore it up a bit (in conjunction with the brittleness you get from electrifying/arcing enemies your armour penetration will be a lot better).

For blessings take Superiority, it gives you the most consistent buff vs massed enemies on higher difficulties, and Riposte. Compared to Shred, you lose only 4% crit at max stacks and if you miss a swing with Shred your stacks disappear. Riposte will always be active when you need it as it gives you 16% crit immediately on dodge.

Use the single target mode for flak targets and up. Against maniacs you're better off cleaving with the default mode and throwing in chordclaw axial slashes.

Ranged: Arc Rifle.
Take extra damage vs flak and extra damage vs maniacs. If you're going to change one of the two, change the latter. Flak is hands down the most useful damage type on this weapon as the arc hits the torso, not the weakspot, this means enemies with carapace or unarmoured heads like scab maulers, scab plasma gunners, dreg shotgunners and dreg gunners will take extra damage from the arc. You also get extra damage when headshotting scab ragers with the actual shots themselves.

For blessings take Enhanced Voltaic Arcs and No Respite. 

The arc rifle will basically demolish any targets you fire at while also debuffing them with brittleness from the Retribution Conduit talent (goodbye carapace), leaving survivors vulnerable to your whole team's arsenal or your melee weapon.

Gunsmith is a must to counteract the arc rifle's slow reload. If pressured, you want to weave in a few chordclaw slashes and kite, then start blasting again. 

Ability: Chordclaw.
Take Axial Slash for sweeping elite clear and making space. Take Slice and Dice to amp up your chordclaw's cleave damage in situations where you need to spam it. 

You can take Satiated Steel instead of Slice and Dice if you tend to space your chordclaw uses out, just note the buff will overwrite itself in situations where you spam the ability so you will lose out on some capacitance ticks. Satiated Steel is an entirely fair choice however, and if you pace yourself it will probably edge out Slice and Dice for elite clear (though not boss damage).

You want to be using your chordclaw about once every ten seconds in combat to maintain your damage + other buffs and capacitance recharge, then more often to quickly dispatch elites like maulers, crushers and bosses. Even with the slash, you'll often stagger crushers, though obviously you want to use the single target attack to yank their tainted soul out and delete them from existence. On auric packs of maulers can easily be mopped up by the slash after an arc or two or just throwing a second slash.

Blitz: Artificer Servo-Skull with Noospheric Command.
As you earn a lot of capacitance back from the Redline Capacitators keystone, and the other capacitance talents including Capacitator Reclamation Loop, you can afford to use Noospheric Command to deal with distant threats or eliminate a priority target. It's handy for vapourising anything that isn't carapace very fast. You can also use it it stack a boss with burn quickly for additional boss damage.

The Medicae Servo-Skull can be worthwhile; Purgator is not worth it with organised groups in its current state imo, especially since it shares its grenade charge pool with the Medicae Skull.

Keystone: Redline Capacitators.
We take this for extra toughness damage resistance, capacitance generation and strength. You want to maintain five stacks in combat, hence why you should use chordclaw at least one every ten seconds. Capacitory Limit Override helps the transonic blades but doesn't do much for the Arc Rifle and can be skipped if using the mechanicus power sword in favour of e.g. Adaptive Combat Calibration.

The main alternative as far as keystone go is Flensing Protocols for Higher Purpose, as it gives you absolutely ludicrous ability charge regen. You will, however, be held back by your ammunition if you go totally ham with your Arc Rifle, a bit like that one meme.
Still a solid choice for higher melee attack speed and crit especially if you want to learn into your transonic blades more. Taking Enhanced Capacitance Protocols will allow you to replenish you stacks instantly using the chordclaw, if needed.
Killing 20 elites (18 with CDR on your curios) gives you a full chordclaw charge back thanks to Higher Purpose.

Other Talents:
Retribution Conduit is a must-have as it buffs your damage by up to 35% if you have all 5 ult charges up. We take System Shock mostly to reach this node, however the latter also has the added benefit of making arc rifle soften -> switch to transonic melee to finish off a viable way to conserve ammunition.

Gunsmith is imo a must for the arc rifle to circumvent its slow reload; if pressured you can weave in a few chordclaw slashes, then start blasting again.

Last Stand Relay & Flux Conduit have good synergy with the transonic blades for giving you extra ult generation and TDR, however you can drop these if you take a low finesse melee weapon (you'll want to get some extra toughness gen/TDR elsewhere if that is the case however). The Arc Rifle doesn't really benefit from crit as much apart from triggering these talents, from my testing the arcs do almost the same damage on a regular hit as a crit.

Ammunition Deposit is mostly taken because of having few talent points to spare and imo the rending from Foe-Render Creed isn't doing much for the Arc Rifle. The extra rending is also not noticeable on the mechanicus power sword. 
However, if you adapt the build to lean harder into the transonic blades I do recommend taking Foe-Render Creed as you do notice the extra rending when using them.

Capacitance Reclamator Loop works on arcs and is also a solid choice on the transonic blades. 

Curios:
Apart from CDR, I personally like stamina regeneration as it reduces both the stamina regeneration delay and increases the rate at which it regenerates. 3x toughness for aurics or 3x5 health to eat extra bleedthrough on havoc (I still have to test this build there) are good choices, or swapping one toughness curio for a health curio.
The final perk slot is your choice.