Lilly is best, no question. She has a lot of love to give, but is disciplined enough to raise a child properly and not spoil it.
Emi would be second best. I imagine she'd grow up to be a lot like Meiko, with her daughter developing similarly to herself. Not perfect, but still a really great mother.
Misha would be alright. Her depression would rub off on the child in the form of odd behavior, which may give them trouble. If she doesn't get her lust for parfait under control, she, and thus her child, could be living rather unhealthily.
Next is Hanako.
She will never get over her anxiety, and it will, ineitably, sprout in her child as well. She'll have a hard time not spoiling the child, because the love she'd get in return would be too tempting, and finally, she'd never be able to support the child during puberty due to not having had a healthy youth.
Shizune is second worst.
She'd be a helicopter mom, constantly belittle her child and scold if for getting an A- rather than an A. Her child would grow up with no confidence, and have mommy issues out the arse.
And last, sadly, is Rin. And I am saying this as a Rinfag.
Her mindset is not that of a mother, she could love the child, yes, but not take care of it, both physically and emotionally. Being quite different from anyone else mentally would make it hard for her to understand and help the child during troublesome times.She'd lack the ability to enforce dicipline when needed too. Rin would make a fantastic aunt, as she's fun to hang around and spend time with, but a terrible mother.
And in case Miki and Suzu are relevant: Miki would be the same as Emi pretty much, while Suzu would be a middleground between Hanako and Rin.