Roose Bolton? Littlefinger? Mellisandre? Varys? Who will it be?
Personally, I'm throwing in with Roose Bolton. He's so much more unambiguously evil than all the other characters. He's as clever as they come, and doesn't take half the risks that Littlefinger takes. Perhaps most important, he recognizes the power of magic -- and this is borne out by his regular leechings and his taking Qyburn into his employ.
Littlefinger, we're already clued into his schemes. Ditto Varys, if his epilogue soliloquy is to be believed. Mellisandre, we get a PoV chapter of her. Roose Bolton is still a mystery to us, and there's no doubt he's keeping something (or more likely many somethings) up his sleeve.
Edited by BinkyBonks, 28 May 2012 - 05:05 PM.