I think Judy Collins has proven, over time, to be the most enduring and perhaps the most talented. Joan Baez certainly brought folk to the masses.\, and I do admire her social activism. As for Carolyn Hester and Buffy St. Marie, I just don't think they were ever in the same league. Neither is a very good singer althought St. Marie wrote some good songs. A good question but hard to answer because of all of the women not mentioned.....Odetta, Peggy seeger, jean ritchie and so on.