Probably Zetterberg or Kronwall. Lidstrom said himself that he wants it to be one of them.
I would have wanted it to be Datsyuk, to honor what he's done for the franchise (ever so slightly more than Z in my opinion), but I figure Lidstrom knows the locker room environment better than we all do, so I trust his judgment.
I will be shocked if it isn't Zetterberg. Datsyuk with all those media responsibilities would be amusing for us on HF, but I think that's asking too much of him. Kronwall wouldn't be a bad pick either.