I have always been a fave of Cloud with Tifa...she just seems to care so much for Cloud and his well-being, whereas Aeris seems to act more immature (even though she is "supposed" to be older than Tifa in the game) in the fact that she acts like a giddy schoolgirl who has a crush on a man she finds attractive, and is rather trying to "push" herself onto him to go out with him, where Cloud does not seem to share any interest for her except as a friend.