It requires more trust and communication than regular sex, and oftentimes your SO is sacrificing some of their comfort and possibly dignity to give you pleasure. Her willingness to do that for you is a big turn-on. I like being in control, and fucking a woman in the ass is basically as submissive as you can have her. As for the raw physical characteristics of tightness and friction, vaginal is better in the long run. No pressure, just teasing. Every day the lunch lady gives you an apple and an orange, and then tells you not to eat the orange. Both totally awesome, obviously. From men that have anal sex with their wives, to guys that try it early on in the dating session, these stories capture the essence of the sex act. In porn, however, the attraction to anal is different for me. I wanted him to stop the whole time, but I was too scared to say anything until he asked me. I think another thing is a certain level of trust that must be present, and that she trusts me to not just drive it home at the starting gun. I have met a few women in my time that truly liked it and I think they liked it for the same reason. Plus, when a woman is into it, the feedback of the pleasure she gets as well is mind-blowing. Plus nothing says I love you like allowing me to stick it anywhere I want. So I think there is a primal, biological reward system for a man to want to be with a woman in all ways and mix with her completely. Also, I just love the way a woman looks with something penetrating her lovely asshole. But honestly I prefer the usual hole a lot more.