Why is Crisis Core on that list? That's certainly one thing I hope will be retconned by the VII remake.

Anyway I'd choose either VIII or IX. Both games had issues with their gameplay that could easily be fixed by a remake, plus they'd look just as beautiful if not even more so than VII if remade with HD graphics.

Honestly speaking though, Square needs to spend more time and money coming up with new ideas instead of recycling old ones.