Longbows are better if you do not use the crossbow expert feat. If you do use it, hand crossbows are better. Many ranged builds use this feat, even for the "you can attack without disadvantage at close distances" thing alone.
Hand crossbows deal 1d6, which is 3.5 on average.
Longbows deal 1d8, which is 4.5 on average.
That is 1 damage less on every attack... Does not really matter.
Most of your damage on ranged builds comes from Sharpshooter (+10 to every attack!) and stuff like that.
Sharpshooter:
"You have mastered ranged weapons and can make shots that others find impossible. You gain the following benefits:
- Attacking at long range doesn't impose disadvantage on your ranged weapon attack rolls.
- Your ranged weapon attacks ignore half cover and three-quarters cover.
- Before you make an attack with a ranged weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack's damage."
One benefit longbows have over hand crossbows is range.
Hand crossbows: 30/ 120
Longbows: 150/ 600
Ranges in BG3 have generally been reduced, so these will likely not be the numbers in the game. The first number is the range in feat you can attack normally, the second is your maximum range, but you attack with disadvantage. Both in feet.
Ranged characters will almost always take the Sharpshooter feat. That means you can attack at long range without disadvantage. So 600 feet for longbows and 120 feet for hand crossbows. A lot less, but generally, still more than enough.
So if you invest in the crossbow expert feat, hand crossbows are almost always better.
Otherwise, longbows are better, because of the range.
And, notably, another thing we can not predict of course is how many magic items will be in the game. What is the best longbow? What is the best hand crossbow? Those things matter, of course
