They are all No. 1, for me. It's strangely crowded, at the top.
For Eiza, I like the idea of Cat getting more screen time but I think she is going with Luna.
Luna doesn't want/need anyone, but her having to take care of and teach an assassin (who, presumably, has more skills than shown in attempt on MC's life) will maybe help her to get in touch with some "caring for others" emotions, that she's afraid to acknowledge.
Plus it will help Eiza's training greatly.
Not saying Cat wouldn't, but there's maybe more of a gap, with Luna, for her to fit in?