I'll go Santiago, because they have three other lefties that are solidly in place-
Sale (true ace)
Danks (unmovable contract right now)
Quintana (two solid seasons under his belt, and controllable for years)
Erik Johnson will be in the rotation, and they can have Rienzo or a cheap free agent signing compete for the 5th spot.
So Santiago would make sense to move now as a piece to get some help on offense.