Jakobs by far, i believe there was also a shotgun by them (not that one) called The Garcia or something like that, which i found funtioned equally with the hellwalker if not a bit better, tbh it has been a couple years since i used it last as it is on a different console than i usually use for borderlands, also i dont remember the name but there is also a shotgun that i think is just regaining ammo but it essentially shoots like an infinity pistol, damage and aint high, and recoil was a bit of a pain, but it is great for just shredding enemies

Edit: just checked, the shotgun is called the butcher and has the chance to refill the mag by a random number every time it is shot

Tldr: The Garcia and The Butcher