The Ballistic Fist is definitely powerful but I think (not sure though) the Thermic Lance might be able to out-damage it. The Holorifle (and to a lesser extent, the Multiplas Rifle) is a faster-firing but lower damage per shot alternative to the Gauss Rifle, and Big Boomer does significantly more damage per shot when compared to Dinner Bell but can fire only once before reloading. Other good weapons are the Anti-material Rifle, Medicine Stick, Christine's CoS silencer rifle (or This Machine or Paciencia if you don't want to carry around 2 sniper rifles), Annabelle, Thump-Thump, Tesla-Beaton prototype, and Pew-Pew.all of which use different ammunition.

There's a youtube video showing where it's at as well which is what I used to find it for the first time.

There's a YCS/186 Gauss Rifle available at a mercenary camp east of Brooks Tumbleweed Ranch that does more damage than the regular Gauss Rifle but isn't available if you have the Wild Wasteland trait since the merc carrying the YCS/186 will be replaced by an alien captain carrying an Alien Blaster instead (the Alien Blaster is guaranteed criticals though, so it's still one of the best weapons).

Best gun fallout new vegas