Diablo III: Reaper of Souls

As a Demon Hunter, when you have end-game equips, what combination is better, dual wielding crossbows, crossbow + quiver or bow + quiver?

I don't think there's anything better than the Legacy Manticores with 2 slots + the new Dead Man's Legacy quiver.

Legacy Calamity with a Radiant Star/Marquise Ruby + Quiver is competitive with 2os Manticore. The strongest Legacy Bow is Windforce, and I don't think it's very competitive unless you have a 2.0.1 Strongarm's Bracer.

In 2.0.1. the best bow is probably Kridershot. Longshot/Unbound Bolt and Venomhust/Sydyru Crust might be able to roll well enough to compete. Kridershot allowing for a 300% Generator makes it significantly more powerful in that regard, even if it might roll lower than the other bows; except it autorolls DEX and a socket as well as its damage.

Buriza's special effect might make it competitive with certain builds. I don't think Manticore, or any other Crossbow rolls enough damage to compete. It seems they use the same damage range as Bows, meaning they're 1.4/1.1x weaker. Depending on how Demon Machine's explosive bolts function, it might be good though.

For Hand Crossbows, the new Calamity is decent. Dual-wielding Danetta's looks like it would be good. Any other DW combination is probably not worth the loss compared to using a good quiver. The damage rolls on Hand Crossbows seem to be enough to compete with Bows.

The new Quivers are actually competitive with Legacy Deadman's Legacy (lol) since they can roll such a high amount of DEX for damage to compensate the best Deadman's 300/300 DEX/VIT rolls. Black Bone Arrows can random roll up to 524 DEX and have one more random roll. These particular ones are craftable, and have 3% less max IAS, but compensate with 4-7% Elite Damage as well.

I think overall, Hand Crossbow or Bow with quiver is the better choice unless you're comparing a rare with a legendary. The only reason I would use a Crossbow is if I wanted to guarantee an OHKO with an attack/have higher damage per cast instead of damage per second.
This is using the data they provide in the game guide, so the damage rolls for Crossbows might be wrong on there, though as far as I am aware, that information is pulled from the game's own database.