Many great but Wellesley most prestigious
I think most of the original seven sisters are comparable in terms of academic rigor - Smith, Wellesley, Barnard, Bryn Mawr, etc. But I think Wellesley has the most widely recognized alums over the years - Madeleine Albright, Hillary Clinton, Cokie Roberts, Diane Sawyer, Nora Ephron, Linda Wertheimer, Madame Chiang Kai Shek. Each school also has its own stand-out departments. If you're trying to decide which apply to, it'd be important to decide on the mix that works best for you - the rigor/reputation of the depts you're interested in and the type of location you want - urban, surburban etc.