It totally depends on the quality of the singer's voice. Doesn't really matter to me if they are male or female, as long as I think they sound good/unique/interesting...
...That said, I would like to hear more females in visual kei, cuz like 99% of VK bands are male-fronted. Jyou of exist trace is THE singer who got me into VK-style music in the first place (back in 2009) and I haven't been able to find another female singer like her. I've tried out a few other female-fronted bands and either I don't like their voices that much, or their sound is more power metal (one of the few genres I really don't like).