I'm having trouble with this one actually XD
If we talk pure farming it's between Muramasa and Artoria. However, factoring CQs I think it's between Ibuki and Okitan. I'd give the edge to daishouri thanks to the def buff removal, which can bypass even Castoria's true invulnerability. Both can also loop, so my question is how easily can Okitan loop? I don't have her nor Skadi, so if somebody could give me some insight that would be helpful.