I have maxed out both hawkmoon and fatebringer. From a pve perspective, in my opinion fatebringer is the better choice. In terms of raw single target dps, the hawkmoon does shine, but the lack of ammo can be pretty brutal in the harder modes. Fatebringer has arc damage, explodes and reloads faster with crits (the explosions are after every kill so its pretty awesome), is only legendary, and has roughly 40 more shots than hawkmoon with the field scout perk. What i haven't tried yet is hawkmoon with an ammo perk on my armor. Running around vog looking for white boxes on the ground all the time is what pushed me towards fatebringer initially.