My girlfriend explained to me that anal is physically more pleasurable for her, to the extent that vaginal penetration is disappointing. However, it is not a turn-off; this is to say that when given the choice, she would choose anal, and if not given the choice, she gets annoyed that she has to settle for something lesser.
I personally find both anal and the idea of a woman being turned-off by vaginal penetration to be very arousing. But I’m not about to complain that my girlfriend only views it as “less good” rather than “bad”.