Being on the bisexual side, I have two. I like smart chicks for one. I don't know; there's something about a nice pre-making out talk about anything ranging from game theory to literary analysis or just plain old geekery with someone who gets it that turns me on. The girl's appearance helps a little, but it's not that much of a factor for me.
Then, on the male side - comfortably overweight men about twenty to thirty years my senior. That, a nicely tailored suit and a clean look? Fuck it, my hind brain takes over. It's a lot less intellectual and a lot more physical, and I haven't found guys that pack that appearance and pair it with an interesting personality.
Of course, it might help if I were more into both sides' respective dating scenes - but I'm not. I prefer chance meetings and more organic and natural means of getting to know someone. I've tried my luck in a couple gay bars and hated the type of guys who straight-up came forward to introduce themselves. I hated hetero bars for how you're more or less expected to try your luck with the laydays. It's like casual sex is the first step of a relationship, instead of a confirmation that something serious might exist between two people. It bothers me.