Questions on bows

I've long been confused about the modifiers on bows so if someone could clear this up I'd be most grateful. Which is better and why? A crossbow that is +165 DB21 MD+20 or a +163 DB22 MD+20? Finally, when a crossbow or any missile weapon has major, epic or legendary bloodthirst, does that number add to the damage bonus or the damage modifier and how are the final stats of the bow calculated? In the case of a legendary bloodthirst cantrip, +10, does that add to the damage bonus or the damage modifier?

Thanks :confused: