I see both girls getting bashed, recently though it seems Tifa has taken over the spot light. It used to be pretty equal, but lately all I see is Tifa hate on the net. 8I In any case, all reasons for hating both girls are pretty damn stupid. I get disliking a character just because they aren't the type of character you like, but hating a character for reasons that make no sense? Nah. Explain yourself and do it right, or gtfo. (meaning, back up your reasons) I don't think you should have to explain why you like or dislike something, but if someone's genuinely asking you because they're curious, if you get all huffy and defensive it's kind of a sign that your reasons are bs.
For Tifa it's because she's a slut, a liar, treats Cloud like crap, is jealous of Aerith, and is desperate.
For Aerith it's that she's annoying, a stalker, a boyfriend stealer, overly flirtatious, clingy.
None of those things ever made sense to me.