I'm pansexual, but to keep things simple.. With Men, sometimes it's hard to tell. Sometimes looking at a guy just 'does it' for me. Or their smell... so I know some of it is hormonal. Otherwise, maybe just because they're so different from me, and therefore are a bit interesting. Beards, I've learned, are nice too. Height, muscles, etc. Nice things too. I guess there's no real mysterious reasons for liking them at all. It's all pretty typical stuff. And well, a big reason is penises. Or I hope it's a big reason...

However, men also frustrate the crap outta me a lot of the time for various reasons. Plus they scare me sometimes. My boyfriend sometimes gets this rage built up and when it comes out, it's very frightening. So that's the downside to masculinity, and their size and muscles and all that. Nice when they're on your side, protecting you, but not when they could potentially turn against you...
As for women, I'm simply much more attracted to them physically, and have a broader range of 'types' that I like. Women are beautiful. But beyond appearance, it's nice to relate with women mentally and emotionally. Women are also generally cleaner and nicer and gentler, which I like. So I lean more towards liking women. And someone brought up the point that men make them feel more feminine. Well, I could relate to that at first, but now.. There are times I actually want to butch it up a bit. Not necessarily because I want to be a 'top', and not necessarily to attract more femme women (because I like butch and anything in between too), but I guess maybe I've gotten past that need or desire to be with men as a counterpoint to feel more secure. I'm secure enough in my femininity that I don't need the contrast to feel more like a woman. Hopefully I'm not offending anyone with any of this, just my own personal feelings and observations here. Anyway, my attraction to women has also changed as I've transitioned. Took me a while to figure it all out and I still haven't completely. But my former attraction to women was based on being 'a guy' and now it's very different. So I'm still getting used to liking women as a woman, but I really feel that I would be happier in a relationship with a woman.