I went to Bnos Chava and loved it. The teachers are AMAZING. The girls are a big mix–some more yeshivish and some less, mostly from Bais Yaakovs, plenty from out of town. The staff really cares about their students. I graduated more than 15 years ago and they still keep in touch with me and my classmates.
I don’t know much about Bnos Sara but I know the em bayis well and she is wonderful. I can’t add anything else.
The proximity to the dining room is not relevant. BC is in buildings 5 and 6 and BS is in building 7, right next door. The difference is insignificant.