What do you think is the coolest designed sci-fi gun?

I really like the Aperture Labs portal gun.

It is a cool 50s design, round but sleek shapes

Noisy Cricket

I always loved the Needler from the Halo series. It was a really unique design at the time and probably the most fun I've had with any weapon in a first person shooter. Also, the explosions and the ching it does when reloading is just perfect.

While I never got into Halo, I have allways liked the Needler's design, it looks sort of biological...
- All of the Covenant designs are meant to be very organic looking. In the novels, the ships and such are described as "looking like undersea predators"
obligatory hyper

Deckard’s gun in Blade Runner was always my favorite. Somewhat uncanny because it was clearly sci-fi, but retained that hard boiled detective aesthetic, like you misremembered a noir shootout.

I have way too little knowledge about the genre in general but there was something oddly satisfying about the Service Weapon a.k.a. Director’s Gun from the Federal Bureau od Control..

But I am guessing the part of using it as a game mechanic makes a big difference, there were plenty cool looking things in movies or series — but this one just jumped first to my mind.

The Service Weapon was awesome. It's got an intense sort of gravity around it. Hell, the first interaction with it is fighting a battle of wills in order to not shoot yourself in the head with it. The gun itself doesn't look all that impressive but I do think it's neat enough, and if you look at it from the perspective of the Service Weapon being a character in the story of Control, it's really, really cool.
Came here to say this. Somehow looks brutalist in a hard sci-fi way, while also giving Eldritch vibes.

The entire game just oozes style
I can see that, though I have allways thought it was a bit too chonky
- 6 different guns in a such compact form factor for a price of not dying while being chosen to actually use it, with a tiny little perk on the side of automagically becoming the Director of the Bureau with the side hustle of talking with Paranatural Entities/The Board — how’s that too chonky?
- This guy has Trump hands

The pod gun from Fifth Element is one of the most interesting from both a design and an effects perspective IMO.

Ah, the Zorg ZF-1, nice one!
- Four full crates, delivered right on time! What about you, my dear Aknot, did you bring me what I asked you for?

They crazy gun from The Fifth Element.

The ZF-1. [activates a ZF-1 and holds it] It's light; handle's adjustable for easy carrying; good for righties and lefties; breaks down into four parts; undetectable by X-ray; ideal for quick discreet interventions. A word on firepower. Titanium recharger; 3000-round clip with bursts of 3 to 300. With the replay button, another Zorg invention, it's even easier. [lights reveal a mannequin in police gear] One shot... [shoots mannequin]...and replay sends every following shot to the same location. [turns around, shooting in the direction of the Mangalores; bullets curve their trajectory and hit the mannequin instead] And to finish the job, all the Zorg oldies-but-goldies. [fires every weapon at the mannequin as he mentions them] Rocket launcher... arrow launcher, with exploding or poisonous gas heads, very practical... our famous net launcher... the always-efficient flamethrower, my favorite... [winks to the Mangalores] and for the grand finale, the all-new 'Ice-cube System'! [fires a cloud of liquid nitrogen which freezes the remains of the mannequin. Mangalores applaud politely by carnage]
- Now a real killer, when he picked up the ZF-1, would've immediately asked about the little red button on the bottom of the gun...
- You forgot to mention the 'little red button' :) - Well played for putting his whole monologue here - I was going to suggest that gun.

The Callahan Full-bore Autolock "Vera"

Well, my days of not takin' ya seriously are certainly comin' to a middle.
It has extreme sentimental value

I’m partial to the Judges’ guns, particularly from the Urban-led movie, as I’ve not delved much into the comics.

Also, I think this falls more into the fantasy category, but I love the chonkiness of Hellboy’s Samaritan.

I'll take the boring route. I respect the gun design of the N7 weapons. They look like futuristic versions of our current weapons but the paint design is on point.

I was wondering if anyone was going to mention Mass Effect.

Always been a big fan of all the shotguns. Specifically Geth Plasma Shotgun.

Fuck. Too many choices bru.

Halo's OG AR, the MA5B has that utilitarian look to it, like the rest of that universe. I like that because it feels realistic in a way (think of the utilitarian designs to the armor and vehicles in Aliens, for example.)

The railguns in Eraser, with their oversized x-ray scopes. Nothing special in retrospect, but I thought they were awesome when I saw the movie in theaters.

Weta Workshop has put out some cool-looking stuff. The Chemrail in Elysium for instance. Although, I think I'm more enamored with the in-universe lore of it. From the fandom page:

It is a dual-stage weapon, use chemical propellant first and then electromagnetic rails as the second stage.

Pretty cool actuation! That and the Lightning Gun from Unreal Tournament 2003/2004 are the only two with memorable (lore-wise) firing mechanisms for me. Here's the Lightning Gun's:

Once the target has been acquired, the operator depresses the trigger, painting a proton "patch" on the target. Milliseconds later the rifle emits a high voltage arc of electricity, which seeks out the charge differential and annihilates the target.

Design-wise though, I think Weta's weapons in District 9 were more appealing—more exotic, u noe? E.g., the ARC gun, and the Repeater.

I think the District 9 designs must have influenced the weapon design in the Titanfall franchise too, and I like the weapon designs there as well. The Flatline is maybe my favorite pilot weapon design (not to use though). Charge Rifle is pretty cool too though, with the 'breathing' capacitor banks on the sides. Titan-wise, gotta be Tone's cannon, hands down.

But there's so many more!

You only had to mention UT2004 to get my attention, design wise, the Lightning gun is great, I like the yellow shell and how the lightning emitter moves between shot, but for actual gameplay, I am definately a flak monkey.
A regular sci-fi gun sommelier.

I want to toss the Type-2 phaser from Star Trek (circa 24th century) as my personal favorite. It has this design which reads as a tool more than a weapon, which I love.

The iconic and tastefully restrained design of the Blade Runner handgun https://www.imfdb.org/wiki/(Blade_Runner)_-_LAPD_2019_Blaster

I want to toss the Type-2 phaser from Star Trek (circa 24th century) as my personal favorite. It has this design which reads as a tool more than a weapon, which I love.

I prefer the retro aesthetics of the TOS Type 1, especially for the integrated Type 1, but regardless, it's an excellent choice for the reason you state: it's a very versatile tool!
- You said Type-1 (the compact, key fob looking TOS phaser), but linked a picture to the TOS Type-2 (the pistol). Which did you prefer?
  
  I love the concept of the Type-1, and it would definitely be my favorite pick of the phasers based on function. But for how it looks, I like how the TNG Type-2 kinda blended the TOS Type-1 concept as a tool, but sized it up to the TOS Type-2 pistol in size. Best of both worlds. Still feels like a tool, but more power drill, less garage door opener or handgun.
  
  EDIT: my autocorrect kept messing up the link.

I don't even like the anime but the Dominator is now my favorite one.

From a novel so you don’t get to actually see it, but the clockwork diamond pistol from Chasm City always caught my imagination. Mostly transparent and needs to be key-wound.

For one in visual media, the 5th elements Zerg ZF-1 pod weapon, obviously.

I'm rather fond of Murphy's burst-fire pistol and hide-away leg holster in Robocop. If we are talking the coolest gun, it's got to be the Zorg ZF-1 from the Fifth Element.
https://grabcad.com/library/zorg-zf-1-with-shutters-1

Zat'nik'tel from Stargate SG:1.

First shot stuns. Second shot kills. Third shot disintegrates.

Michael Shanks disagrees with calling the penis gun a good weapon.
- I love Daniel Jackson but Michael Shanks is such a d-bag in basically every interview (and there are some very questionable "behind the scenes" stories about him...). In that clip he somehow manages to be the most obnoxious Comic Book Guy fan ever.. while being on the stage.
  
  The 1-2-3 is REAL stupid, no arguments there. Well, specifically, the "3 shots disintegrates" is. The 1-2 is not. Killing someone with a "less than lethal" weapon is just reality. And you can potentially get some real awesome moments when Teal'c or Ronon show how much of a beast they are by tanking multiple zat shots before succumbing.
  
  But also... the 3 is incredibly useful from a narrative perspective and is the same reason that Starfleet uses phasers. Having one prop that can fulfill multiple roles and act as a "get out of plot hole free" card (as mentioned with hiding the bodies) is incredibly useful narratively.
  
  All that said: I do love that the Tau'ri were very clearly about "more dakka". Insert meme about Starfleet being afraid to intervene with other cultures and Stargate wanting to get their Nic Cage on.

I don't know if anime counts, but the Psycho-Pass "Dominator" is a really cool science fiction concept in itself.

You can't mention the dominator and not add a gif of it moving from non lethal to lethal mode
- Hey, power that thing down!
Especially when it changes between the three modes (non-lethal, lethal and destroy-decompose)

All the Warhammer 40k guns are pretty thick.

Someone needs to go through and add inline images to each of these

You're someone!

The Laptop Gun from Perfect Dark

Spetsdöd.

I guarantee you've never heard of it because it only appears in a series of novels by Steve Perry, the Matador books.

The gag is, it glues to the back of your hand. The barrel runs along your index finger, and you fire it by pointing your finger and touching the barrel tip with your fingernail.

It fires microdarts which can have a variety of effects, the #1 use being a drug called "Spasm" which makes every muscle in the body contract involuntarily, leaving the victim tied in a knot for 6 months.

The original trilogy of books:

The Man Who Never Missed
Matadora
The Machiavelli Interface

Then solo books after:

The Albino Knife
Black Steel
Brother Death
Churl

Prequels:

Omega Cage
The 97th Step
The Musashi Flex

I'm a big fan of the Matador series. I was surprised to find that another had been released. "Churl" apparently did not get much fanfare.
- Print on demand through Amazon, he doesn't have a publisher for it. It's about Dirisha and Geneva's kid. Oh, yeah, they have a kid now. ;)
I am a Swede, and while I have indeed never heard about the Spetsdöd gun, I can tell you it would translate into something like:

"Point of death" or "Death point"

The mechanics sounds similar to the SCP skeleton bow...

It’s simple but sleek - the WESTAR-34 blaster pistol that Jango Fett uses in SW Ep 2.

Also looking up the name made me realize that this website exists…seems like an IMDB wiki of movie weapons:

https://www.imfdb.org/wiki/Star_Wars:_The_Prequel_Trilogy

The IMFDB entries for older shooters really show how many misstakes they made, look up Fallout 3, Fallout New Vegas, Half Life, Half Life Opposing Force, Battlefield 1942 and Battlefield Vietnam for some good articles

NGL I really dig the Blade Runner Pistols

For me it has to be the PPG from Babylon 5, it is small, but looks like it has some weight to it.

I'm going OG - the Buck Rogers disintegrator gun.
(See: Foo Fighters self titled release)

As much as I didn't like the game, the MagX guns in Starfield are pretty dope.

The flesh guns in eXistenZe are also pretty rad.

The Zorg gun is cool, but I always liked Judge Dredd's more. All the same multivariety of fire modes, but in a compact handheld design.

Yes, the Lawgiver instantly came to mind!

Two of my favorites are from books and don't have pictures: the nanotech weapon given to grunts in "Old Man's War" and the Soft Weapon from Niven's short story titled, appropriately enough, "The Soft Weapon". There was an animated Star Trek episode based on The Soft Weapon, but I can't remember what I looked like, I just remember the producers weren't brave enough to animate an alien with two heads and three legs.

Other than those, I really liked the silly guns in Ratchet and Clank, epecially the Vacuum Cannon.

I was an eldar player back when I played WH40k, but the tau railguns are such a great bit of visual design. Perhaps amplified by how terrifying they are to be on the receiving end of.

Destiny 2 has some great ones. I always liked the design of the Sleeper Simulant.

Destiny has so many amazingly designed weapons. Thorn, Malfeasance, Winterbite, Touch of Malice, all the Ikelos weapons, Conditional Finally, Deathbringer, Eyes of Tomorrow, Gjallarhorn... Weapon artists at Bungie are on another level.

I'm noticing a distinct lack of BFG

The BFG exists in several versions:

The original from Doom 1993 is just a rectantular box with a weird handle, the sides of the box is covered with techno pixelart, but nothing striking.

The Doom 64 version is very similar to the 1993 version.

The BFG in Doom 3 has a profile of a weird space potato: https://doom.fandom.com/wiki/BFG9000/Doom_3?file=BFG9000-BP.jpg

The ingame model is more like a rectantular box, but with an updated case: https://doom.fandom.com/wiki/BFG9000/Doom_3?file=Bfg3

In Doom 2016 is has a better styling, with an actual grip, it now actually looks like a gun!

In Doom Eternal it looks great, if a bit generic, but not bad.

The BFG does exist in Quake II and Quake 3 Arena, but the design is just terrible.

So while I like your enthusiasm, I don't share your oppinion on the design of the BFG series.