I don't believe it is a choice. I believe it is a combination of nature and nurture. I have never had the least bit of physical arousal from a woman--in fact, a picture of a naked woman will instantly deflate the hardest of erections for me.
I had a gorgeous female friend years ago, and she once climbed on my lap in a bar and started kissing me out of the blue one time. I had never been kissed like that in my life, but as much as my mind understood that she was the ultimate kissing partner for sheer technique, it was like my body was completely disconnected from the experience. And she had a gorgeous face and perfect figure, so if she couldn't inspire an erection, no woman could for me! After that we made out fairly regularly, but it was fun in a non-sexual way...I guess not fair to her, though, since she WAS turned on by it.
Of course, it sucked for me too, in a different way, because in all the years since then, I still haven't met anyone else who can kiss like she could.
Back to choice--as much as I don't think I ever made a choice, if science ever allowed us to change, or if a genie (lol I'm not superstitious and don't believe in genies) were to give me three wishes, I would never choose to NOT be gay. I don't know if that's because I am a defiant person, or if it would be a matter of rejecting part of who I am, but as much shit as we go through in society, I wouldn't really wish away my gayness.