I prefer Aeris, and this debate is pointless, Neither is particularly incorrect, although Aerith is the official one. There are debates about whether the tetragrammaton (god's name in the original bible scrolls) should be translated Yahweh of Jehovah, It's all really inconsequential, although making a decision on whcih one to use is still difficult. Don't go arguing about which one is 'right'.

Also, Aerith is more original than merely naming here after a star-sign