I am pansexual/polysexual. Which means more or less I am attracted to who they are not what they are.
I think Little Ming & AndreF have both given good points.
I have had relationships with men, women, transgenders and everything in between. I have even had a semi relationship with a gay guy (don't even try asking me how that works, it hurts my brain)
What I found is I had periods where I would swear off a certain gender or type because of a failed relationship. "I hate blondes" or "I'll never date women again" lol, etc.
I also am more comfortable with men simply because I grew up with guys, know how they think and my natural flirting instincts work with them. With other genders I am unsure, so those relationships fell in place almost accidently, they were just natural extensions of other relationships (friendship, acquaintances etc) but that does not mean I loved them any less. Actually my two most meaningful relationships before my current were with a women I lived with for a brief period, and a transgender person I fell head over heels for. I am just simply a little more awkward/shy in those relationships.
I am now married to a man, but it could of happened that I ended up in a relationship with anyone.
I suppose I have said things along the lines of "I identify more as straight/gay/ etc at this moment" but have still checked out people outside those genders.
I think really it would be more of a "I'm having a more fulfilling relationship with
this person right now" and it may happen that the next relationship is with that gender too. But its not really something I think about.
I've probably just confused you more