I would prefer Joker not have a homosexual fixation with Batman. He can still have an unhealthy obsession, but not erotically. While there have been good representations of Joker where they have hinted at some sort of homosexuality, I always found it much creepier if he showed no signs of sexuality at all.
A common link between all people, whether heterosexual or homosexual, is that they are still attracted to others, and this isn't just with humans either, it is with almost all of the animals in the world too. By having Joker not actually desire any form of sex in any way it alienates him even farther from humanity.