I say Rebekah, coz she's been there done that, seen it all and actually knows what it means to be human. Elena is a joke really, and the proof is simple, when it was Damon and Stefan's life on the line she spilled the beans of Esther's plan to save the two getting rid of Finn because it was 'safe', in the last episode she was the mastermind of another vampire genocide when she put Jeremy up to killing Kol.She cares about no one but herself really.
I think for some reason the cure is a ruse and so the status quo will remain, but if indeed Silas has the cure.I expect a wicked twist in the end, and someone who deserves and wants the cure wont get it.It may be a precious caveat for example that since Elena is a doppelganger once she is cured so is Katherine and I doubt Katherine would want to be mortal,I think Katherine may sabotage the plan. Or in fact while Silas out of spite may cure and Kill a werewolf Klaus, as Klaus originated the Salvator vampire line, all vampires of his line including the Mystic falls clique will be rendered mortal so the season may end with the Salvator brothers ,Caroline,Katherine and Elena mortal. Damon wont be pleased about that either. That would be an interesting twist, the possibilities for an interesting season 5 are certainly there.
What do you think?