Used to consider myself 95% straight, and 5%... unknown. Now it's about 50-50, and that's the influence of testosterone. Strange as it seems, T made me more into guys, and I guess being married to an mtf made me more into penises... but that's another thing entirely (or something... awkward silence...).

I dated a ton of guys before transition (and yes, I'd say it was definitely a TON), but never really felt anything for them. I could get attached emotionally, but the physical attraction was only there with a couple... and funny enough, they were gay and bi. The girls I dated, on the other hand, were somewhat distant emotionally, though the physical attraction was very much there.
I think, if I weren't married, I'd be searching for the near-impossible: a girl with male parts. Is it possible that my perfect woman could have a penis? Well... I married one... but I can't imagine spending my life with a guy. I could have one-night stands with guys. I could play the field with guys. However, when it comes to a soulmate, I think they'd have to be female.
I think, if we had a way of surveying every ftm on earth, we'd probably find an overwhelming number of bisexuals, with the rest split near evenly between gay and straight. But I wouldn't worry about what everyone else is. As Shakespeare said, to thine own self be true.
SD