I personally liked Aeris like twice as much as Tifa, so I would’ve chosen Tifa to go.
So questions like this baffle me. It’s like saying should Vanille and Fang turn to crystal in the end of FF13 or Hope and Snow, or something. These things happen because the plot entwines its way for it to happen.
If you’re asking based on how useful they are in battle, well I personally liked Tifa’s limit break much more than Aerith’s, so my decision works Aerith dying regardless.