Boss hunts, it should be pretty obvious that bow > xbow
Like vasu said, NPC xbows > bows in terms of damage up until a certain amount of time, when the bow speed finally kicks in. In AoE's and short fights, I see no point in using a bow. I'm going to be spamming skills anyways, so the speed doesn't really matter. In bosses, your skills take a while to cool down, so bows will be better than xbows (NPC) when it reaches a certain time. KQ bosses are good examples of this~ o:
Besides for looks, I've never really used a bow. Kinda pointless IMO, because once I finish spamming skills in my order, the mob's going to be dead anyways so I never get to fire many regular shots.