Wow! So I just found out that stating a preference is sexist. Full disclosure, I love female vocalists. Generally, more than male. Alison Krauss, Emmylou Harris, Eva Cassidy or Jennifer Warnes have the ability to tug at my soul far more than any male vocalists. Don't get me wrong, I like all.
As for a preference, who knows what's at play. I grew up in the 50's and 60's listening to classical music at home and rock when I could. Peter, Paul and Mary rocked my soul back then and inspired me to become a fairly proficient guitar player. That said, I never really got the Beatles or Stones. Why? beats me.