I think its Daenerys. Melisandre said that the prophecy says the hero will be reborn amidst smoke and salt, and she interprets this as pointing to Dragonstone, but I think that the smoke and salt refers to the Daenerys's tears and Drogo's pyre, which Daenerys entered as wife of the dead Khal and exited as the Mother of Dragons. And even if Melisandre is right about the smoke and salt referring to Dragonstone, that is where Daenerys was born. Also, Melisandre kept trying to get Stannis to allow the use of his bastard nephew's blood to wake dragons from stone, whereas Daenerys already has woken dragons from stone