I would prefer 1 or 2 for the simple reason that they effect the game on a more play to play basis. WR success is so dependent on so many things. O-line and D success open up every facet of the game. If the o-line is great then running and passing(regardless of who the targets are) becomes easier, thus giving your defense more rest/better starting position. A better d forces the other team to react to you, gives the offense more possessions/better starting position/less demand for points.
While a stud WR would be great for me it ranks below the need for o-line and lb help.