I suggest the Dwarven Hand Cannon.
The Ancient Bone Bow adds just a little more then crit %. As of now, your agility adds double Ranged Attack Power, so your Ancient Bone Bow actually gives you 22 Ranged Attack Power, as well as some extra crit %, along with extra dodge and armor.
However your Dwarven Hand Cannon has more base damage, so therefor your Aimed Shot's as well as normal shots will hit harder. Not to mention the occasional proc, boosting your DPS up just a little more. The DHC is also slower, allowing even more damage done then the ABB.
Just my 2 cents though. I'd personally go with the DHC over the ABB.