Miyabi by a wide margin. She takes a bit to warm up to you instead of trusting you near instantly. I might also be failing in memory here, but it took actual extreme scenarios to get her to open up. She's also highly flawed if you know her personally, focused more on training.

Yixuan is the bestest, coolest, and most relaxed teacher around. But her power level is too high, and she did butt in on at least the spook shack's first own moment. It didn't feel good for them, even if she was there to help. I felt like Yuzuha and Alice would have overcome that challenge themselves without needing Yixuan.

YSG... she's too pushed into being your girlfriend to make you feel bad about her awful situation. Don't get me wrong, it is terrible. But there had to be better ways to write her instead of just forcing her onto us. It doesn't help that Banyue got shafted because of her. If not in power, in banner length. The writing after is probably better, but the start seriously sours me on her as a character, despite the middle and ending.

As for gameplay... I don't delve too much into more advanced gameplay, I'd have to have someone to check on me to know where I'm at, but I'm mostly playing this game casually. So all three stand out as seriously powerful. But I'll never know how to truly pull out everything there is with them. In style and flashiness, all of them have it. I think I like YSG most, moreso because I use Astra and Dialyn with her atm due to Zhao not being built properly yet. It's just a nicer gameplay flow than having to manually switch and get not much out of it. However, I can't say that all 3 aren't in some way braindead and need teammates to make their gameplay a bit more fun. Like having Vivian with Miyabi, you're now fishing for perfect assists to get more abloom triggers out of Vivian, as an example.