I must be the only one who thinks that Tifa looks better in her AC appearance. Black hair > Brown hair, she has a boob reduction (which I thought was necessary), and the appearance simply matches her personality better. Tifa as she appeared in the original FF7 just looked like a total prostitute, and prostitutes turn me off. I'm sorry.
Aerith is still better than Tifa. She's got a better name, she can cast magic better, she's more relevant to the storyline of FF7, everyone rage-quitted when Sephiroth killed her, and she freaking stopped Meteor (with a little bit of help). Oh, and did I mention? She's hotter! (No justification required or necessary.)
And Tifa? She didn't tell Cloud about the Nibelheim incident until after Sephiroth screwed him up, she freaked out like a mad chicken when Cloud went into a coma, she travels the whole world looking like a hooker, and she had a sad little slap fight with Scarlet when she could've just Dolphin Blowed her off the cannon, killing her and averting the Proud Clod battle later -.-' Also, her skirt's super short, but we never see anything underneath. What's up with that?
Sephy-san > Kefka
Aerith > Tifa > Yuffie
Yuffie sucks. Don't even make me go there.