This is a really interesting question. I always go trousers for an interview to ensure there's no criticism (too short, too tight, too dowdy) or accidental underwear reveal. I'm a girly girl so just can't hide my femininity much, but there are interviews I would be careful to appear less girly.
Who to be interviewed by is difficult. Some women can be more competitive or plain hostile than a man would. But some men just don't like or respect women, some totally hate us. Men IME are more likely to assume a woman is going to be off because of children. It really is difficult, and one I can't call at all.