It seems to me, based upon the standard affection values put into the game, that the developers meant for you to end up with Aeris on the date. It could be argued that the developers then meant that to signify that Cloud and Aeris are supposed to end up together, or it could simply mean that they wish for you to learn more of her story before she departs. She is something of an enigma even if the player does try to learn everything about her, and if the player just 'plays' through the game, not really reading into the story, having the pre-set could aid, I'm not sure. I have to admit, it has been some time since I last played FFVII, so perhaps my thoughts are occluded.

And for the original meaning of this thread, it is so very personal... For me, personally, I would say Tifa and Cloud, but that is only because I like Tifa, and I actually hate Aeris. I truly didn't feel much of anything when Aeris died besides,

"Damn... I hope I can still keep the materia I had on her..."

It's just personal preference, and because of that, I have managed to always have Tifa's affection values higher than Aeris' at the point of leaving Midgar.

I'm curious about the idea of going on a date with Barret... My, how would that play out?