Non-relative, for me it's a tie between Kotal Kahn and D'Vorah.
Relative-wise, for me, tie between Jacqui and Takeda.
Kotal, D'Vorah and Jaqui are tied for me at the top spot, though.
Erron Black and Ferra / Torr are also awesome in design and gameplay (IMO), and I hope that they return in the next game, but I feel like I still don't know them enough to like or dislike them.
I absolutely love that MK introduced a gay kombatant. Especially with the surge in open hatred for the LGBTQ community (which is bull....) I 100% support NRS' decision to create a new character like Kung Jin.
I'd say D'Vorah, but they literally just copy-pasted Tanya's entire background onto her with the whole treacherous woman secretly working with Quan Chi/Shinnok routine, so I've gotta say Cassie since she brings a bit of interest towards the story.
But if you mean which is our absolute favorite, Ferra/Torr. I love playing as them. Never get bored.