Actually, Scav would probably win now that I thank of it. He can force you to reroll your hits, and he has AOE arm debuffs.
That's cute, Conquest is like +4 basic against the Cryx one. Plus cheap boundless charge and Curse of Shadows.
In a way their feats are almost exactly the same. Both have -1 cost, and boosted magic attacks. Scarveous has rerolls built in, and can channel. He's weaker in melee, but can stand back. The jacks have near identical ranged weapons, though Kraken is more accurate and faster, while Conquest is Stronger and a bit tougher. Now I'm interested. Assuming the lists are:
Witch - Conquest - Conquest Max Mechanics Max Mechanics
Both are 55 points. Mechanicks have better healing (24 vs 16 on average), but the Krakens can dodge better, since they slightly outthreat Conquests and requires 6s to be hit by them. Really, its a case of "what else is in the army" because if Scav has a good Soul Harvester target or a Wraith Engine, it would swing the results.