Just about any weapon of the Warhammer 40K universe takes the cake.
The Bolter being a miniature missile launcher launcher that fires like an assault rifle, each bullet a small rocket for maximum impact and damage.
The Chainsword being a chainsaw combined with a sword.
The Orks have a gun called the Shokk Attack Gun that sucks in tiny Gretchins (mini-Orks) and then teleports them through The Warp in the general direction it is aimed at. Sometimes resulting in the small Gretchin, who just travelled through literal hell and saw everything that awaits poor souls who gets there, to end up appearing INSIDE the armour of unfortunate, for example, Space Marines, where the batshit terrified little thing starts trying to clawing it's way out of the inside of whatever it is.
The Eldar has a D-Cannon, the D for Dimensional, that shoots a miniature black holes.
The Necrons have the hots for something called the Gauss Rifle, a anti-molecular gun that rips shit up at the atomic level, disintegrating things into dust.
When everything fails, the Imperium of Man deploys their last resort weaponry in a move called Exterminatus. Using weapons like the Cyclonic torpedo that burrows to the core of a planet, exploding and destabilizing it, often resulting in the total catastrophic structural failure of the planet and wiping it out. Or the Virus Bombs that contaminates the entire planet with a Life-Eater virus that infects everything organic, melting it down to a sludge that then evaporates into a gas that once it reaches a critical point, self-ignites and covers the planet in a cleansing firestorm that eradicates all life and oxygen, turning the planet into a barren rock devoid of ALL life. Or they just orbital bombard the shit out of the planet like a giant carpet of lasers and all other manners of weaponry.
Shit like this makes the Deathstar look merciful.
Out of all that, I think I'd go also with the Bolter, it's big, it is loud, gets the job done and is a series staple.