It really depends on the person. Male or female? Coming or going? Standing or sitting? Tall, short, slim, stout, mode of dress, etc.? The human eye is naturally drawn to bright colors and areas of high contrast (fun former-picture-framer fact), as well as movement. So, if the hair is a fiery red or kohl-dark eyes are set against a pale complexion, those features are likely to attract one's attention first, unless something wiggles or jiggles and thus catches the eye.
I saw a woman last night at a thrift store. I
think the first thing I noticed was her hair: long, luxurious, tumbling down in wave after wave of dark brown curls. She had a lovely smile, too, which she threw my way once or twice. (
Or did she?) Ultimately, though, my gaze lingered elsewhere.
Were she another woman, I might have noticed first the shape of a leg or the fullness of a lip. Had she been a man, I might not have noticed at all.
Of course, if the person in question is leading a full-grown ostrich on a leash through the frozen foods section of a supermarket, then it's the shoes—always the shoes.