Personal taste, to me brother/sister is the least exciting variation of incest (unless is really well written, and it's about older sister/younger, cheeky, horny brother). The reason i don't find it exciting is because there's no age difference, and because i simply believe it's the most common incest in real life, i guess there are really plenty of real-life cases, so that's kind of taking away all the taboo and morbidity and excitement, at least for me.