FFS for sure. A major portion of how people read you is your face. With a very feminine face I think you would struggle to pass as male many times, even if you tried. So, basically it comes down to me wanting to feel completely comfortable around other people as my highest priority. I'm rather perceptive and I can definitely see those inquisitive looks on people's faces and I know exactly what they are thinking. I think without FFS only a very, very small percentage of MtF's can pass by their face alone.
Everyone has a different view on it though. I'm kind of a tomboy I suppose you'd say, and acting super girlish and fake just so people accept me as female is not something that sounds that fun to me. That's just not me. I want to act the way I want to and wear what I want but still be accepted as female by all. FFS can in all likelihood give me that.