Referring to them by their family name seems weird to me. I think Ruki is prolly top tier, at a glance. Range, speed, parry that gives you backstub opportunity, counter super, super that shocks, good high-low mixup...she's pretty mean. I'm not really a fan of Madoi though. She requires relatively strict spacing for a good portion of her B moves and she hits like a mosquito. *shrugs* Not my girl, I guess.
Oh whoops I got one of the names mixed up from not playing in a while. I don't play Madoi, but I play Minami like you. I dunno how many people you've played but whenever I high parry an attack, my parry gets... counter parried? And I end up eating another combo. Other than that I like her a lot more than the rest of the cast. Her damage output is stupid. If you land a hit and they don't burst out, you have already almost ended the match. Not too mention it's pretty easy to hit confirm since she only has a good few pokes, but each of them have massive hitstun.