The difference between Tifa and Aeris can be almost directly related to where you first meet them at. Where they either work at or where they spend alot of their time at.
I think the image that alot of people have of Tifa that she was a slut and things can be based off of where you first meet her at. The Seventh Heaven Bar. You can say it relates to how she dresses. But I think it is based more along the lines of where they had you see her first at.
And along the same lines for Aeris. The image that people have of her can be directly related to where you first meet her at. At a church.
People generally give the symbolism of Aeris that she is not necessarily one who puts out. But that she is one who kind of plays games. Hence which is kind of a symbolism somewhat of a church girl.
I think the game makers had you meet the two girls in the locations which you did for very specific reasons.