Well I think it's more complicated than that, and actually all three (medical condition, lifestyle choice and movement) apply, in some way or another. Cause the way I see it being trans and dealing with that situation entails several different aspects:
1.) Psychological, by which I mean anything that can be construed as gender dysphoria, gender euphoria, the wish to transition, the wish to pass and/or live as the other sex, etc. Not everyone refers to this the same way, but you get the gist.
- I think that at least the dysphoria part here is a "medical condition," but just wanting to be true to yourself, isn't necessarily. This entire aspect is quite individual, I believe, and I don't think it's a choice.
2.) Transition which is the action of making changes to your life to improve it gender-wise (often to reduce dysphoria and be true to yourself) which is anything from presenting as the other sex, name change and pronoun change to medical stuff like hrt and surgeries, to also legal stuff like changing the gender marker.
- I don't think it's entirely incorrect to call this aspect a "lifestyle" although that term has negative connotation (as to imply it's not a vital choice) and I don't call it that (I simply refer to it as transition), but in the sense that it's a way of life that most people do not embark on... sure.
3.) The social consequences. By that I mean anything from stuff like facing transphobia from friends and family, coworkers, strangers on the streets, etc, to bigger scale issues like bigoted laws and widespread transphobia, and much more. Issues like these and more is largely why the trans community started.
- The trans community (or the T in LGBT) in this aspect is what's considered the "movement," generally. As in being trans isn't a movement, but fighting for our rights and more acceptance is.
But to answer the question of if simply being trans - and not the consequences of being trans - is a movement, lifestyle choice, or medical condition: I'd say it's a medical condition.
