Should I pick up Phil Hughes(SP, NYY) and Drop Jacob Ellsbury(OF, BOS) or Ian Snell (SP, PIT)?

My outfield is stacked so I don't need Ellsbury but his BA is Wicked Awesome. And who can't resist picking up a SP for the NYY. Ian Snell is ranked about the same as Hughes but is proven at the MLB level. IDK, help me out.