Well, I'm a bit picky but Zoro hasn't get any power up yet, he first needs to learn how to wield Enma properly, at that point, with that new skill or improved haki control, he will be stronger.
Anyway probably Sanji in a way. I hate Oda make him power up through an external device he has to do nothing to get, all advantages with 0 effort, yet design wise is good while Zoro gets a new sword (which is pretty much the same as the others designwise) and Luffy gets a new (another) form of attack.