Khem is my personal favorite. I'd marry him if I could. His storyline is great with you gradually earning his respect - this being a creature that basically views you as food at first - and at the end, was goddamn amazing. Not to mention his own story and how it ends.
Xalek seems like he's not going to backstab you despite being your apprentice. I can appreciate that. Or maybe he's just more cunning than me and I end up with a lightsaber through my face, I can't really be sure about my fellow Sith. Oh well, that's how it goes, if he pulls it off he's earned it.
Who do I not like?
Ashara. I could only tolerate that terrible twi'lek by reading the romance as my inquisitor ruthlessly manipulating her. She has absolutely nothing interesting to say and I'd sacrifice her loving arse the first chance I get.
Vette. Yes, please give me rage-fueled warrior a quirky, snarky idiot who disapproves of everything I want to be as a Sith. That doesn't feel limiting at all.
Corso. Creep-tastic, even as a male smuggler.