Sunkeeper is usually the better choice. You can have physical on bracers, amulet and shield. It's unlikely that you have elite dmg at all. So with elite dmg the 27% dmg increase is effective 27% dmg increase for the "important fights".
With Doombringer you have effective ~10% more dmg from physical and the vitality, which is something like ~2% dmg increase from thorns.
For any speed farming like 75+ you might consider using sun keeper as you will kill most of the elites. As for hard progress 85+ you might consider using doombringer, because of this a bit of survi, and the fact that you will probably skip most of the elites. But it depends on your playstyle and will to skip blues and yellows.
With enough cdr you might consider droping cdr on ammy for the vit, or on the shield for the socket.