To me, Stastny makes the most sense. That or a defenseman. But there is no centre in the farm system that has a chance of becoming a no.1 center, except perhaps Kadri, but chances are slim on that happening. He can score, he's good on faceoffs, a good playmaker, and he'll cost only money.
However, I actually voted for Vanek. I think you have to at least talk to him. Our top four wingers are generally very good, but we need one more and I don't know how you can pass up the kind of talent he has.
Third choice would be Ehrhoff.