Crossbows deal consistent damage (Dwarven Crossbow deals 30-30) while bows have a variable range (Daedric Long Bow deals 1-50)
So one isn't necessarily better than the other.
I usually always stick with the bows though, as I tend to use them for precise long range attacks, where I have time to pull the string back fully.
But the crossbow loads fast and will deal much more consistent damage, especially in close range combat.