Well... That's a tough question, since I pretty much play anything, but I'm not really a fan of VN's with rape in them. While I do play r-18 Visual Novels, I generally try to achieve a good ending, WITHOUT Rape or anything of the sort, it just turns me off. I also hate VNs who have incest-related things, it makes me feel awkward... (I have two brothers, so I can't even IMAGINE engaging a romantic relationship with them, that's just... Yuck).
That's about it, I don't mind playing anything, excluding rape and incest-related stories. Since I told you my preferences, mind sharing yours?