Bows shoot faster than cross bows and are quieter. That's pretty much it from what I've seen. I guess since they shoot at an arc a little they have more range but frankly I don't see a difference and I shoot just fine even a mile away with my crossbow.
Crossbows do a little more damage but mainly their advantage is a much harder hit where with Power Shot they stagger everything almost all the time. They are also an ammo weapon meaning they are actually faster than a bow when it comes to the first shot at least which is usually most important. Also cross bows have a built in ignore armor effect too. People have said this doesn't make a difference but I hugely disagree. It doesn't matter when fighting creatures, dragons, mages, etc but u always notice a substantial increase in damage against any armored humanoid opponents. It DOES make a difference against the right enemies.
As for bows being quieter I find that makes no difference at all once you get muffle and your sneak skill is higher.
Now for me I prefer cross bow just because it prefer the look and feel of an ammo weapon. I remember when I first played Dawnguard and Isran handed me the cross bow. Initially I was like what but when I armed it and shot I thought "Whoa! It's like I have a gun now!"
But in the end I don't think there's a huge difference in over all fighting power compared to a crossbow and bow. In the end it's more likely just about which one looks cooler to you. And for me it's hand down the crossbow.