While a lot of people have recommended solid "meta" bowguns, I'd like to highlight some hidden gems.
Tzitzi HBG: If you wanna be a "support" HBG, this is the one to pick in my opinion. Loads a lot of Sleep1/2 ammo, can use Para2 in a pinch, loads the most Recovery ammo of all HBGs, and you can use Elementless with it (one of only 5 HBGs that can do so). Limited to Normal2 as your primary ammo, but that's not awful. Somewhat counter to my recommendation as "support", Tzitzi cannot use Demon or Armor ammo.
Jagras HBG: In the process of looking for an alternative to Nergi for Spread ammo, I took notice of Jagras. While you do not get Spread3 like Nergi, you get twice as much Spread2 and Elementless. Notably this is the only HBG that can't use Wyvern ammo (as an aside, Teostra is the only one that has 2 Wyvern capacity).
Pukei HBG: This is basically a worse Legiana (same Piercing capacities but doesn't use Piercing 3), but gets Wyvernsnipe instead of Wyvernheart. If you want to embrace your inner sniper or just use "budget Legiana". Other pros include an extra deco slot (level 2) and 2 more augments than Legiana on account of being Rarity 6.
Tobi LBG: While this is already notable as a great Thunder ammo dispenser, it's also worth nothing that in the process of using Recoil mods for your Thunder ammo, you will also be able to shoot Recover ammo while moving. Tobi also unloads Poison2 fairly well, making this a doubly good weapon for fighting Kushala. Also (again, on account of the recoil mods) functions as the probably best Piercing LBG, able to use Piercing2 on the move. Finally, it's also fairly nice capacity for Para1/2 ammo. This is definitely more than "just" a Thunder LBG.
Lavasioth LBG: Like Tobi, this is notable as a good elemental bowgun (Fire in this case) with a couple other cool niches. It is one of 3 LBGs (including Vaal and Dragonbone) that can (potentially) shoot Dragon Ammo while moving, loads a decent amount of Sleep1 as many LBGs do, and has a nice 2 level2 deco slots to work with. Normal2 as "basic" ammo of choice.
Honorable side mention to Rathalos as the other Fire LBG that boasts higher attack and 20 affinity.
Jyura LBG: Same as the last 2, it's more than just its element. Best LBG for Sleep application and can also make use of Poison and Para. Has the same "shoot Recover Ammo while moving" thing as Tobi above. Can use Spread2 as your "basic" ammo, and can also use Demon ammo.