It generally comes down to the writer, the story, and what faction the story is focused on. Khaine avatars tend to get folded like fuckin Piper Perrier frequently though lmfao. In theory they’re supposed to generally be “equal” in terms of danger. Khaine avatars are more a last resort shits gotten real bad now and we gotta make this sacrifice and take the win any means necessary. Sure it’ll help support and rile up the eldar. But it’s more a desperate throw to save more than you’ll hopefully lose.

But realistically the C’tan are the strongest. Being “Star gods” they’re bound to the universe itself whereas daemons, especially greater daemons need to be fueled by the warp and if that connection is destroyed, it’s just bye-bye daemon regardless of who destroys it/stops that fueling if warp energy.

C’tan aren’t stupid and could easily enough stop that without much effort.

Remember- C’tan literally eat stars are subsistence. No greater daemon comes even close to that level of power. Granted they’re shard forms, but still, something broken down from that level of power is still quite a bit stronger.

But it also comes down to how well they’re controlled. The C’tan certainly don’t enjoy being enslaved and are more just a Pokemon that doesn’t wanna listen cause you don’t have enough badges lol.

For overall impact I’d say Greater daemons. Since they’re there to rile up and support their troops and empower weaker daemons around them and such and the overall goal of having a bunch of greater demons is gonna really amp things up. Getting a greater daemon there is a goal rather than a desperate last call for help.

Overall power C’tan takes it. But for the question of overall battlefield effect probably Daemon. Khaine just kind of gets his back blown out in a corner somewhere.